I wish I had remembered this last fall — but, better late than never, huh?
I just put my kid to work helping with the family travel budget, and it was surprisingly easy.
The U.S. Department of the Interior, through the Every Kid in a Park program, has made available a free national-parks pass to the family of every U.S. fourth-grader. All they have to do is go online here, and play a "game" in which they answer about two questions, and voila! A printable park pass is made available. Ours says it's good through the end of August, which is perfect since we are about to set out to see Crater Lake, Oregon Caves and Redwood National Park.
A beginning-of-the-year fourth-grader can get a pass valid for the whole school year, but this will work great for us. With homework on the wane, I had secretly hoped that this activity might involve a bit more effort — at least writing a sentence or two, for example — but all my daughter had to do was type in her zip code, assert that she was in fourth grade, then make two choices that involved clicking boxes.
The website does offer plenty of information and trip-planning resources.
An annual pass to all national parks is $80. (Active U.S. military members can get them for free.) An annual pass to just Mount Rainier National Park is $55, and a one-week vehicle pass is $30.