You just need to lower your expectations a bit. I keep a Molly, several Platies, a couple of crayfish, a Rubber-Lipped Pleco, and have had several Fancy Guppies in my 55GAL tank with my 3 male Map Turtles. The key is to go with cheaper fish that you like and to not put anything in the tank that you don't want killed and eaten. With that being said, I've had really good luck keeping the Fancy Guppies and Platies with them. The Molly has been in the tank for 4+ months. The turtles will occaisionally chase them, but quickly learn that they can't catch them. I may lose one fish a month, if that. The Platies really bring a lot of color to the tank with their reds, oranges, yellows, and blacks. What I have noticed, however, is when I buy feeder guppies, which are much smaller than the fancy guppies and platies, the turtles are really good at hunting them down and eating them. What dooms the feeder guppies is both their size and their tendency to hide in the nooks and crannys between the large polished river rocks that I use for gravel in my tank. When the turtles prowl around on the bottom and poke around in the rocks, they trap the feeders and get an easy meal. I haven't seen the two crayfish molt yet, but I have a cave for them to do it in. I did lose a small freshwater mussel to something, not sure what.
So, I would either put much larger fish than the turtles in the tank, or go with $2 or less fish, so if you lose one, you're not out much. They provide a lot of stimulation for the turtles and and to your enjoyment of the tank with their bright colors. I'm currently trying to breed platies in my map turtle tank. I have 6 females and 2 males. When the babies are popped out, they hide in my gravel and give the turtles something to eat and chase. I saw my first platy baby getting chased around in the gravel by one of my Mississippi Maps this past week. It was fun to watch.