I recommend consulting a locksmith before ordering a new lock... the dust cover is replacable and if the lock cylinder is in good shape the wafers can be replaced and you'll save a ton... granted you'll only save a ton if YOU pull the lock out and take it to him.... if he has to pull it or come and get it... well...
The mechanism is obvious enough once you get the interior trim panel off. IIRC, the center panel is all you have to remove. The cable which runs to the front of the cabin to release the trunk from inside may have snapped. If so it can be a bit of a pain to replace and you might want to consider just installing an electronic trunk release solenoid... it's not aly less of a headache, but they're nice if you've got an aftermarket alarm with a trunk release feature and you'll be pullingup the carpet either way.
Cables are shown here:
http://www.cygnusx1.net/Supra/Librar...spx?F=6709&P=1