Double-checking is always good
I went to National and plugged in 2 weeks (May 15-29) in a Trailblazer and my quote was $3,111. Quite a difference!! I encourage you double-check on this with National to make sure you don't get hit with a nasty surprise when you get there.
Also, that is without paying the fee for the 24 year old to drive. If you elect to not pay this extra fee for a younger driver, you sure better not let that person drive. If something should happen while that person is driving, it could really come back to bite you.
It also doesn't include the extra insurances, etc. You may not need them but all drivers will want to check with their own auto insurance provider to ensure that your own auto insurance covers rental vehicles. If not, you will need to pick up that extra coverage.
I'm assuming you have done your research about Route 66. If not, this page will be really helpful.
Tim mentioned that your food budget might be a tad low. A good way to save money on this, and still eat well, is to eat out of your cooler.