If you are comfortable on your bike with running shoes on... and that is how you have trained, DO NOT change it up at the last minute. Train like you race, race like you train.

Learning how to ride with clipless pedals/cycling shoes will probably add more stress and money... that it will be worth to you. I say this because you said that you won't be doing this that much.

This past weekend, I observed a duathlon, and many of the competitors wore their running shoes on/off the bike... no cycling shoes. They still did a great job and didn't come in last.

I would also ask you how much you are cycling, outside of competition. I love my cycling shoes... but then again I ride 30-100 miles a week. When you ride that much, you want clipless pedals. If you don't ride that much, then why bother?

Do your first sprint without them. If you *feel* like you need them... then you can upgrade later. For now, don't worry about all the details... just go out there and have fun... and race like you train.