To be honest, we haven't had that many people here have this sort of problem. My own PSP (bought directly on launch day) is still going strong. Considering what you found out for the costs of repair compared to the new one it would be worth the while to just get a new system and the full warranty that goes with it.
I would be a bit leery of those power boards you find online- there's no guarantee those are actually fully functional, if even for the system. they may well be a scam waiting to happen.