Central Locking - deadlock locked focus w reg?

Can anyone help me before i spend a fortune, i have a 3door W reg focus zetec with central locking problem, keyfob buttons dont work (changed battery, no different), car used to lock itself whenever it wanted during driving etc but hasnt done that for a few months now, but can only use drivers door now to enter car by using keyfob key, passenger door wont open no matter what is tried (either pressing button to unlock position on inside, key in lock on passenger door - nothing works) tried spare key in case that made any difference, boot release button doesnt work have to use key to get into that as well. Spoken to garage and they say they'll have to take passenger door panel off from inside, causing damage to it as screws on side of door which you cant see when its locked to get to mechanism, they said it sounds like the deadlock on the passenger is locked/stuck! Any ideas, help, anything's worth a try before i spend money at the garage. Cheers!!