I did a sprint just for fun a few years ago, and because I wasn't sure whether I'd like it enough to continue with the sport, I didn't want to buy anything new just for that race. What I did, I picked my likeliest pairs of cycling shorts (more minimal/less absorbent chamois, more supportive/less saggy fabric) and wore them into the shower to see how much water the chamois would soak up and whether they'd stay in place when wet. The pair I picked worked fine. Then I just wore a sports bra on top. I was prepared to throw on a running jersey at T1, but since they don't require you to cover your shoulders and it was so hot that day, I just did the whole thing in bra and shorts.
Probably depends more than a little on what temperatures you expect.
Speed comes from what you put behind you. - Judi Ketteler