I may sound kinda dumb if you've done this already, but, have you tried spraying wd40 into the mechanism? If so ignore the dummy here LOL
if the wd40 frees it up; find a good lithium spray grease to spray into the handle, and the latch on the door

the door panels come off after the handles and armrests (1screw in each handle 2 3/8 bolts in the armrest GENTLY pry up the chrome ring at the top of the armrest to expose the screw there) once those are off if you have a crowbar (no really trust me) use the flat end to find the clips that hold the panel on put the clip between the fork and GENTLY pry it up
the clips are just held in the panel which is fiberboard.
once you get inside, the door handle is held on by 2 nuts.
Mine used to stick pretty badly too. i was able to use WD40 inside the door to free it up. once it was free i sprayed all the pivots with white lithium grease

Rather than using a crowbar there is a tool called a panel popper that is specificaly made for taking off panels. other than that it is not hard to replace. I have to do the same thing to my dads car.

I strongly agree that you don't use a crowbar to remove the door panel. I found a "panel popper" for a very reasonable price, (couple of bucks) looks like a screwdiriver with a different tip. Make sure you take off the inside "door pulls" also make sure you put the plastic liner back on when your done. There will be two nuts holding the door handle on from the inside. Its a real simple process. Nothing hard at all. I've been a body man most my life if you need any help e-mail me and I'll walk you through it.