When I swam competitively in hs/college I used to wear (and wear out) Speedos pretty quickly. Granted, that was 5 swim practices a week, and now I'm only doing 3.
Since I've started doing tris, I've been wearing a TYR tri swimsuit (has tri padding in it so I can jump right on the bike and ride- yeah right). It's lasted since January, and is still in perfect condition. I should be able to get another 1-2 seasons out of it. I bought it on e-bay for $10. The material is much thicker than a regular swimsuit, as it's made to wear during a tri. Don't know if that helps or not.