I share your pain......I soaked my 3G and turned the indicators white; like you everything worked except the screen, so I could at least back it up before I took it back. Fortunately I'd taken insurance out with CW so got a brand new one in exchange. My understanding is that other bits in the phone will corrode in time so it's not as simple as just having a new screen.
Hope you get it sorted without having to spend to many ££s.