Mobile phone repairs

DomTom

What is the cheapest/best way to get a phone repaired? Mine is starting to get water damaged from using it in the rain. I considered taking out an insurance policy such as phones4u's "policy admin" which seem to cover phones without a proof of purchase ,just a proof of imei usage, but then i saw the excess was £50 which is pretty much what it'd cost to get it second hand.

the damage itself currently:
its on a samsung u900 soul, the back cover starts falling off more easily, on the left hand side of the screen (but not on the screen) there is a purple mark (running most of the length)

as of today, there is a "bubble" of water in the middle of the screen, which floats around a bit.

the phone still works apart frm the camera doesn't seem to work (crashes if i try to go on the "application)