I used to do some data recovery, put an advert up at the local uni, be half decent at it and the money soon comes in. (software only)
The price of recovery depends on what it wrong, if its a physical issue (the heads are knackered/ its not spinning up, the drive electronics are burnt out, etc) your looking at a few grand for recovery, it its just a data issue (destroyed sector, damaged index, etc) Its a lot less.
I assume its pata, (as it is a slave) is it still coming up with drive fail press f1 when you boot?
if so try another channel, but I suspect it won't work... if you still get that message it means its a hardware failure and there is nothing that you can do to fix it unless you fancy coughing up a few grand. (you can try swapping the boards over that works occasionally)
if your not getting that message then you can try software, a good start is spinrite.
For future reference, Raid 5 owns your soul, however raid 5 cards aren't cheap,