Make sure it's unlocked.
Stick a BF screwdriver in there, push the button and pull the screwdriver to disengage the locking mechanism.
It's happened to me on my XJ (cherokee) a few times.
You'll see there is a peg that sticks up in the middle of the floorboard that the door latches onto. Look on the bottom of the door, and you will see the C-channeled locking mechanism. When the lock is unlocked, just put a screwdriver under that sucker, and push the button, and pry it open.
Can't afford Mods? Go To College!