Absolutely can be used in warm water. You need to remember on that first dive if you get a little warm just let some water into the suit via the neck. What some don't realize is that the first dive isn't the one you need the suit for as much as the 2nd, 3rd, 4th, or even 5th.
I take a 5 mil to the Keys even if the water is approaching 80. By the end of a week of diving 3 or 4 dives a day I'm glad I did. A std 3 mil would have me cold by the 4th day. If I were to go back I'd take my 3 mil but also the 2mil shorty I have to put under it and layer with that. If I did get too warm just leave the shorty out of the mix.
As for pricy I don't think so. They are comparable with any other high end suit that MIGHT fit you. The Wetwear one will fit. And their support after the sale is great. I can call and ask to talk to Connie who is the owner and get her on the phone easily.
And their use of rubatex and the nitrogen compressed neoprene insures that your suit is not going to compress as much as suits using std neoprene. That means your buoyancy does not change as much and you stay warmer at depth.