I know this is kind of sad, but my bio teacher had a male florida softshell in a half filled 20 gallon tank for about 18 years in his class room. Poor thing was so stunted it stopped growing at about 6 inches long. No way to get out of the water, no light, no heater, only a little water pump to keep the water from being stagnant Apparently he used to have 2 tankmates (other softshelleds), but he killed them. Luckily the teacher retired and the turtle was donated to a nearby nature center where he went on display in a massive (250+ gallon tank).
I guess what I am trying to say is they are pretty tough animals, but at the same time that was horribly cruel and I hope your future softshelled has a much happier outcome.
As for turtleshack.com, I have no experience with them, but I have heard some pretty nasty stuff about them, so I would try avoiding them. Kingsnake.com is a great place to get one, and most LFS can order them in for you. Also see if you can find one to adopt. I was looking on Petfinder.com recently and was suprised at the number of herps for adoption in my area.