You don't *have* to wear anything special for a tri. Tri suits, tri tops, tri shorts; none of that is mandatory.
I did my first tri without any of those.
Spent a grand total of $125 for my "tri" gear: a pair of goggles and a wetsuit. Everything else was just whatever I already had that worked and I liked.
Wear your tankini in good health! 
Edit to add: I bought my first pair of tri shorts a couple months ago. Still not sure if I like them enough to wear in a tri. We'll see...
Last edited by KnottedYet; 04-29-2008 at 06:35 PM.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson