What is your weight? If you are looking for a thin shorty for warmish water, a very tight fit is not necessary. In fact, a slightly looser suit will be more comfortable, easier to get on and off and might even last longer if you aren't fighting with it every time you put it on. In short, it doesn't have to fit that well.
I suspect you can get by with in inexpensive, off the rack suit.
Also, unless you have an aversion to wetsuits or are diving in water well over 80 degrees, you might like a full one-piece, 2-3 mm suit gives you a little more warmth and full body protection from stingers and the sun on the boat if it is not too hot. A shorty suit has limited use for me, sometimes I wear one over a lycra dive skin.
