As I have memories of road trips that date to the era of .24 per gallon gasoline (.19 once during a gas war in Mississippi) the concept of spending more than $20 per night for a motel room is just a bit difficult to adjust to. So, from that perspective imagine the difficutly I have in spending $50 to $100 per night.
Okay, I know that in the modern era rooms in this price range are considered as “moderate” so lets start from that perspective. Here is my list of where we found a home away from home on the last trip, my impressions, and my suggestions. 
First on the list is the historic Hotel Vendome in Prescott, Arizona that dates to 1917. With tax, our bill came to $99.99, which for the Prescott area is almost a bargain rate.
Hotel Vendome, Prescott
As it is mere blocks from the beautiful courthouse square that serves as a venue for a wide array of festivals throughout the year, Sharlott Hall museum complex and historic Whiskey Row, the location is ideal. As the owners have gone to great lengths to preserve historical integrity without sacrificing the amenities modern travelers have come to expect, the atmosphere and ambiance was most delightful. 
A beautiful neighborhood, including a high end restaurant next door, a wine bar with a variety of craft beers in the lobby, a pleasant but simple continental breakfast, and a pantry with free coffee or soda available to guests twenty-four hours per day round out the package. Overall, we had a very pleasant stay but my suggestion is an upstairs room (no elevator) opposite the side overlooking the square.
Next on my list, the venerable old El Rancho Hotel in Gallup, New Mexico, an icon in the era of resurgent interest in Route 66. Harness the power of the Internet and you will be able to keep the room rate under $100. 
In comparison to the ornate ranch house style lobby, the halls seem almost institutional and the rooms sparse. The bathrooms are almost small enough to be comedic.

El Rey Inn in Santa Fe

Surprisingly, during the 1930’s, 1940’s, and 1950’s this was a haven for the rich and famous as evidenced by the staggering array of autographed celebrity photos on the upper mezzanine, and the names on the room doors.
The on site restaurant is excellent (atole, a blue corn meal, and Navajo tea for breakfast) and the bar is pleasant. This is the proverbial frosting on the cake.
If your looking for a four or five star resort, the El Rancho Hotel will disappoint you. If, however, your looking something unique with a pleasant ambiance and a restful night, this is the only place to stay in Gallup. 
As the destination for day three was Santa Fe, we decided to give the historic El Rey Inn a try. Again, use the internet and you can keep the rate under $100. 
The heart of the El Rey Inn is the original motel built in the mid 1930’s when Cerillo Road was Route 66 that has been refurbished with an eye to historic detail. In 1973 the owner acquired a 1950’s motel next door and combined the two establishments into one complex. 
Again, the modern amenities expected by the modern traveler are available, as is a most delightful breakfast (included in the room rate) that is served on the patio when the weather allows or in the beautiful lobby. All of this, however, is merely just a small part of what makes the El Rey such a special place.
The expansive five acre grounds are a labyrinth of Spanish styled corridors that wind among flower gardens, and landscaped grounds with fountains that serve as a bird sanctuary. 
The El Rey Inn is truly an urban oasis as well as a time capsule.  As it is but a few miles to the historic plaza it is also centrally located to the sites and attractions that make Santa Fe special.
Our next sop was the absolutely delightful Plaza Hotel in Las Vegas, New Mexico. As this is but a very short detour from the pre-1937 alignment of Route 66, or a scenic 100 mile drive from Tucumcari on highway 104, I strongly suggest that every Route 66 enthusiast add this to their list of “must stop” locations. 

The view from my room in the Plaza Hotel. 

Not only is the hotel built in 1882 at a cost of $250,000 an historic masterpiece, it is well managed, spotlessly clean, and is centrally located to one of the most astounding historic districts (over 900 buildings on the National Register of Historic Places). Here is the kicker – our room was $89 for the night but this price included breakfast in the historic on site restaurant overlooking the plaza. 
As an example of how much history is on display here consider that this hotel was the first stop in Teddy Roosevelt’s recruitment drive for the Rough Riders during the Spanish American War, and was the venue for that organizations first reunion. The saloon, appearing as it did a century ago, is where Doc Holiday shot a man during a disagreement in a card game. 

The plaza in Las Vegas, New Mexico

Lined with a beautiful array of late 19th century buildings, Bridge Street, also the original Santa Fe Trail, connects to the shaded plaza. Next to the hotel is a non nondescript row of shops with a cornice added in about 1890. The exact date of construction for these adobe buildings is unknown but in 1846, on the parapet of what is known today as the Dice Apartments, General Kearney announced that the New Mexico Territory was a part of the United States of America resultant of the Mexican/American War.
Our next evening was spent in Santa Rosa at the Best Western next to Denny’s. Even though it is a relatively modern property in comparison to our previous accommodations, it is a bit dated. 

Still, it is always clean, the rates acceptable (especially when one considers that an ample continental breakfast is included), and it is in a good central location on Route 66 that is easily accessed from I-40. For us the bonus is the fact that my dearest friend and I have stayed here so often that when we call, the owners know us and give us the same room.
The last evening of our adventure was the most unusual as it included a campy 1957 movie shown outdoors and shared with Route 66 enthusiasts, and a motel room that was originally a small 1956 Yellowstone trailer. To say the very least, we will have fond memories that spark a smile of our stay at the Enchanted Trails Trading Post & RV Park for a very long time. 
The proprietor, Vickie Ashcraft, has transformed this old trading post west of Albuquerque into something truly magical. While the primary function of the property has been changed to meet the needs of the modern recreational vehicle traveler, it is quite evident that it is firmly rooted in Route 66 history. 
The original trading post, with a few additions, serves as a gift shop, laundry, showers, and lounge. The fully restored vintage trailers near the swimming poo are tastefully decorated with period touches. 

The 1956 Yellowstone, our home away from
home for the evening. 

Again, if your looking for a five star resort, or you don’t have a sense of adventure, you won’t be happy here. As an example, even though every thing was functional in our trailer, including vintage appliances, the owners request that  showers be taken in the old trading post in an effort to preserve the historic integrity of the trailer.
Current offerings for trailers transformed into motel rooms run the gamut from a minuscule Winnebago Dot, to big forty-foot units, and even a vintage Airstream. According to the owner, plans are to make additions soon, including a very rare 1942 model.
As our trailer was rather compact we were provided with more than a few instances for a good laugh. Still, I slept well in, as my dearest friend referred to the Yellowstone, our little clubhouse and awoke with an urge to watch The Long, Long Trailer.
If there was a lesson learned on this trip it would be that if you have an adventuresome spirit, you don’t have to put it away at the end of the day, especially on Route 66. Of course, I already knew that but it was nice to have a reminder every night at the end of a long day on America’s most famous highway.