I'm with the others -- I would definitely think about renting a car. I wouldn't feel comfortable driving an older vehicle across the country like that. The peace of mind alone might be worth it to rent a car.

As for the hotels, I use Priceline. I don't mind staying in cheaper hotels and haven't been "burned" yet. You can even download an app on your phone that will allow you to score great deals.

I love Colorado and think it's absolutely beautiful. BUT, spending some time in Oklahoma might not be a bad thing, because the scenery will likely be very, very different from what you're used to.