I marched in a "Top 12" corps this past summer, and was going into the season with a little bit of financial trouble.
1) Save every penny you get. Birthday money, Christmahannukwanzuka money (let your relatives know what your saving for), pennies you find outside your car, SAVE IT ALL. No late night trips to Wendy's either, it ruins your stomach and your wallet.
2) Go to local, small businesses in your area and ask if they would be willing to help you with your cause. Be sure to be professional about it, dress up a little. I had a deal with a local hair-cut place for every customer that used a specific coupon, I would get $5 towards my drum corps fees. Something small like that can go a far way.
3) If you get a spot with your corps of choice, constantly communicate your situation to the corps management. Also, ask them for ideas, they usually have many great suggestions and keep you on the right track.
4) Hit up your great great step-aunt in-law twice removed. Even if you haven't talked to them in a while, it might be nice to re-establish a connection. Let your far off relatives know what your up too, and even invite them to a show near them over the summer to see what their money is going towards.
5) Contact your local Kiwanis Club, Lions Club, etc. It varies from group to group, but one of them might be willing to shell out $100 or so.
There are many more options, but I have found those to be the most successful. I was able to pay off my entire tuition before move-ins, and even had some left-over money for free-days, and I didn't even have a job.
Good luck, hope that helped a little!