A replacement fuse (Radio Shack/Home Depot) will be really inexpensive. I hav en't broken mine out, but I'm guessing a standard glass tube fuse. You can take it with you or read the rating on it and match it. I would have to disagree that if the fuse is blown you can presume the unit is bad. Several things could blow a fuse and that's exactly why it has a fuse. The fuse is there to protect the unit (and yourself) and not an indicator for unit failure. If it were me, I'd buy more than one replacement, recheck and make sure no salt creep is around, all wiring is both correct and no short circuits and try the fuse. If it blows immediately again, then you could cut your losses and try returning it under warranty or recheck everything for the problem again even deeper.

If the unit's got something else blown, it's not gonna give the fuse a chance to blow again. Replacing the fuse is a really cheap test.