National Park Passfor $80 US gets you, your vehicle and passenger, entry into all the national parks. If you are planning to visit our national parks, this is a good buy.
We spent last year on a journey to and from Alaska. In Alaska we did everything, lots of tours and excursions. We averaged about $1000 a week. I suspect you can do a lot better down here in the lower 48.
Take a look at Passport America and see if they would work for you. One or two nights would give you enough savings to pay for the yearly membership.