The first set of seats I located by calling a local a local bone yard who found a set of 6 ways on their network... for $350. I was nervous about coughing up these bucks sight unseen, so I talked the guy who found them into telling me where they were. It turns out that they were in Grand Rapids, about 100 miles from where I live. Sooo... I packed up the wife and kids in the minivan and headed west, under the auspices of going to the beach in Holland, MI on the big lake. [A few miles out I mentioned that I wanted to stop and check the seats out ;-)]. The seats were in a badly wrecked SSE and were a real mess due to exposure to the weather, broken glass, etc, but the color match was perfect. Because of their condition, I talked the guy down to $160+tax for the set. To make a long story short, I wound up back in Canton with the seats (I did get the kids to the beach, btw)
The two sets of 12 ways were located by fellow MISSLer Mike Mullin, who is apparently a regular at several local used parts places. Since he was not interested in wiring in the 12-ways he turned me on to them for rights to my original set. I bought a set out of a '95 from Schrams in Waterford, Michigan and a set out a '93 at DIX in Taylor, Michigan. I paid around $200/pair for these. The harness and switchpod was had for between $50-$65. The switchpod new is about $115 discounted from GM.
Bottom line is that your best bet it to hook up with the guy behind the counter at a large local boneyard that specializes in late model wrecks and visit often with a box of doughnuts under your arm. When a set comes up, go in and scrutinize them, find out what is wrong with them and haggle.
Back to Bonnville Seat HQ!