Blackberry problem.

[Alkaz]

I have the C8900 and I got it with the trackball, the one with the pad wasnt out at the time and I prefer the ball anyway. Ok, my problem, in June or whenever it was I went to the beach and I got some sand in it and its been working fine for ages now and I've had no problems untill this last week or so. The ball isnt working properly and I have to press it several times for it to do what I want and its slipping and sometimes I cant move the ball at all on the screen which is eXtremely annoying. If I took it into an O2 shop does anyone know what they would do or how much it would cost for it to be sent off?

+ I have no insurance. :(