I'd start out by buying the A.C. maps for the first leg of the journey, and then see for yourself if you find them to be good value. You can always buy the rest later if you want them. One benefit is that they tell you the free places to stay (town parks for example).

For budget, everyone is different and I definitely run high, but I'd say you should do a low and high estimate and then plan for something in between.

Things to think about: 3 meals plus snacks per day. You do need to eat quality food, if you eat crap you feel like crap. And you eat WAY more than in regular life. Camping - at least a few times a week you could get stuck having to pay. You'll need fuel for your stove. Medicine, sunscreen, bug stuff need to be replaced. Getting sick or really bad weather - you might really need to get a hotel room once in a while. You might also want to get a hotel room if you have to spend the night in a big city or in an unsavory area - for your own safety. Mechanical problems - budget for tubes, maybe a tire, and possibly a trip to a bike shop for spoke or drive train problems. You might need to replace or add clothing at some point. Also, plan on having a little fun along the way - a movie or museum, a night out in a bar with a new friend. Also, you might need to visit a doctor or dentist if you're on the road for a long time, even if nothing bad happens.

Anyway, I think I run about $35-50/day, but I don't try to save money other than not staying in hotels too often. I'm definitely the high side with respect to camping touring budgets. I stay in developed camp sites almost all the time, and eat in restaurants several times a week (usually lunch/second breakfast, not dinner). I also drink beer, eat ice cream, buy fancy pastry at every opportunity, etc.