When you say "already assembled", do you mean a clutch kit? Any kit you buy will require just about the same amount of work. All of the standard kits come with the same things: alignment tool, throw out bearing and clips, pilot bearing, pressure plate, and disc, spline lube, etc.
To answer your question, I'd look for a transmission recyling yard. Not sure what to call it, but out where I live we have this entire street with different buildings all assorted to different parts of cars/trucks. I got a replacement ax5 for like 200-300 bucks from them and it's been running great for years. You could also try a scrapyard. Just be smart about your picking if you're buying used. Probably would be best to avoid Craigslist for an item like a transmission. Would suck to put it in and have it grind from the get go. If you're buying a rebuilt or whatever, I don't really have any recommendations because I've never bought one in that condition, sorry.
Good luck.