Depending on how willing you are to spend time on it, you could probably make new ones pretty cheap. What you need is the right sized plywood cut to the existing seat shape, some hinges, high density foam (The Foam Shop - pretty good prices) and some marine vinyl (fabricland I think is where I got mine about 14 bucks a yard) I made some benches for my boat in no time, mind you benches are a little easier than sleepers but shouldn't be all that hard.
Otherwise I don't know anyone who can fix them for you other than a shop, but you could end up spending well over 200 bucks to get them fixed. If you don't care about having sleeper seats you could always buy some captains chairs and mount them with benches or other seats in the back, just a thought though.
If you want anymore info on making your own or fixing your own feel free to PM me.