which seems a bit costly. i'm not really betting on salvage yards in my area, and even if i found one, i'm sure the key would be lost anyway. but i'll check.
my question is whether or not anyone has had experience replacing them, and if so, exactly how much do i have to tear apart my door to fix it?
To remove the lock you need to also remove the trim from the inside of the door - the interior handles, the works. It can be tricky to do this without breaking the plastic hooks that attach the main trim panel to the inside of the door, it pulls upwards once you have removed everything else. the door handle is (from memory) held on by one screw accessed from the inside of the door to the handle, and another two hex-head machine screws from the side of the door - these are under a plastic cap. You then pull the handle free. If you don't have the key, it is possible to transfer the lock mechanism but it is a fiddle and takes patience.
Yes this is a really easy one as jjl said, just unscrew the inside section by the window, then make sure you get all the screws from the door card and slide up. It is a bit of a fiddle. I would keep the window open. Luckily there is a fair bit of room to work inside the doors so unscrewing the exterior handle from the inside is easy. (window up once you get this far of course). Just make sure the new part is for the correct side. Not sure if they vary for the W116 but they did for a different car I bought a lock barrel for once!