first off, whats wrong with the timing? if its just the ignition timing that is out, there should be no reason to change the cambelt, or even go near the thing. how i would go about it is
1. get the fault codes read off the ecu, and then get the ecu cleared
2. get the ignition timing checked, run it for a bit, get the ecu re-read and checked for faults, if that fixes it, then all is well! if not
3. get the garage to check the cambelt timing, to make sure it isnt a tooth out or something silly
i wouldnt expect to pay more than an hours labour to get those things checked out