If you feel like driving to New York I can source, buy, and install you a nice system for cheap
But seriously though, what you've been told is a lie.
The only trouble in installing a new deck is figuring out what factory wires goto what wires on the deck.
Usually It's as simple as looking in your owners manual, online, or in a Haynes manual (free to read at your local library and like 10c to make photocopies).
Even in unusual cases (Ive never done an install on an MR2 so idk if they are an unusual case) it's just a matter of figuring out what factory wires serve what purpose, matching them to the wires on the deck you bought, soldering them up (if you dont have a soldering iron you can buy one of them cold-touch dealies for like $20 which work perfectly and are great for beginners since you cant burn yourself) and mounting the new deck.
Mounting might be a slight problem if it's an unusual case, but usually you can either use the plate provided with the deck you bought, or buy one on EBay for like $5 that you can modify with a dremel and use.
And like Andy said, your other problem can be solved with some time spent on EBay.
All those kind of bits can be had if you just do a search every couple of days.
Even the oddest of parts will pop up eventually.