Roughly £350-500 at an independant, depending on where you go. If yours is a 2.0 16v you'll need to get the balancer shaft belt done too. If you go to any old garage, make sure they have a set of camlocks for the engine.
I do belt/variator changes for about £370 and thats for a 2.0 16v which has a balencer shaft belt to change aswell whereas the 1.8 16v hasn't got a balencer shaft belt so i do these for about £350.
But only do it in my spare time as i work full time at Royal Mail.