Yes, Yellowstone motels not only book up early and are hard to get, they will be the most expensive on the trip along with those in the adjoining Tetons ($160 range). Prices of everywhere we stayed are in our blog. "Bicycling the TransAm Trail" uses symbols of $,$$, & $$$ to give you an idea which are cheapest. I'm sure you can do it cheaper than us, we were more concerned with location (making each day's ride doable distance and hillwise) than cost. Especially if you're a strong rider (could do a big day if you have to) I don't see any problem with leaving camping stuff at home. If you're doing warmshowers, you'll need good phone /wireless service to make your contacts, Verizon works better in remote areas of the west than ATT. And an added perk of motels is most of them have good wireless / phone service even if the phone you bring does not.