I would say to start off with supplements and T-shirts since a sponsorship goes both ways.I think its super generous for you to expect nothing in return but I know a couple of guys sponsored by different companies and they are always advertising for them as gratitude. I would say once the sponsored athlete shows a few good placings then maybe pay for the entries and if any guys have a few 1st place wins,then maybe pay for travel expenses.
On a side note I think MUSCLE-AND-BRAWN T-Shirts, clothing maybe be on way to go in the long run, put cool slogans on the back. Once people start seeing the name more and more, people will start asking questions, inquiring with in and it takes things to the next level. If you look at bodybuilding.com, elitefts,apts prowriststraps, etc, they all have merchandise with the company logo on it, so it gives a sense of pride and gratitude when the athlete wears it.
Anyways these are my ideas on this so far. Sounds like a great thing.