Rob 2-3 liquor stores a day. They usually drop their cash when they get to $100 or so. If you get them right after a drop, you may have to hit a couple more stores. Spread this out over the entire country til you've hit every store around, then start at the first store again.
Otherwise, you could probably make 10 bucks a blow job. If you can fight off the pimps and not become one of their bitches, you will need to blow like 30 guys a day. If you become someone's bitch, then you're pretty much fucked because no matter how much you make, they will leave you with just enough to get cigarettes and condoms. They will even control your crack habit.