How much would a mechanic charge for putting on a door latch?

I have a 1992 astro van and it needs a new latch on the back doors (they will not open). There is only one latch to replace, but you have to get to it from the inside. My brother and I looked at it, and you have to take off at least 6 panels. It looks like it is a lot of work and I need to know how much to expect to pay for it.