Leaving Thursday... BUDGET PANIC! Please help!

[Bre.Kidman]

Hey all. I'm leaving Thursday (7/31) for a solo cross-country extravaganza to "sow my wild oats" before law school. I'm a 25 year old female and I'm leaving from Maine. I'm driving a 2009 Toyota Yaris (super conservative estimate of 35 MPG) and my budget is roughly 3500. I plan to get back by around August 25th. My major stops are:
-Chicago (I have friends to stay with here)
-Denver (Meeting a friend/splitting a room here)
-Salt Lake City (Staying with a friend here)
-Seattle (NO idea where to stay cheap)
-Portland (NO idea where to stay cheap)
-San Francisco (NO idea where to stay cheap)
-LA (NO idea where to stay cheap)
-Vegas (Might splurge and use up my credit card miles here!)
-Grand Canyon/Hoover Dam (Not sure how far apart these are, but planning to get them in here before Texas)
-Austin (Probably staying with a friend, but might be good to get a backup plan)
-New Orleans (NO idea where to stay cheap)
-Atlanta-ish (NO idea where to stay cheap... But if I'm not flat broke, probably a Red Roof Inn!)
-Hustle on back to Maine as fast as possible!

Can anyone give me advice on where to stay in my wild card cities? Any must-sees that I'm missing? I'm open to car-camping, but would rather not be TOO far outside the action... Unless, of course, the better action is at a national park? Thinking about picking up a park pass. Not sure if that allows me to park overnight. Basically just looking for a little advice to deal with my last-minute budget panic. I have a credit card and a few favors I can call in, but would really like to stay on point if possible! Thanks in advance!

ETA: I should probably add that I think I'm decent at long haul driving. I got from Portland, ME to Tulsa, OK in 36 hours and got back in 5 days with a pretty decent amount of sightseeing. I'm comfortable in my car (improbable as that sounds!) and do Chicago in a day (and back in day for a four-day weekend!) at least once a year. I've just never tried anything of this scale before and I'm a little wigged out!