I agree with Jorrell---if you have access to a 3/4 ton pickup and a tow bar, come down to the DC area and buy a 240 that won't start for a couple hundred bucks at a wholesale auction. Check it over carefully, as we have our share of rustbuckets down here too, but with a little patience it should be possible to find a spotless one. Look for an 88, as it has all the same electronics as yours, and a trouble-free upgraded wiring harness installed. Second choice would be 86 or 87, same electronics again but likely has the problematic wiring. If you have an updated harness on your car already, that might not matter so much, and could be another way to pick up a nice car for cheap if the wiring is shot.

Look at the website http://www.wadeauctions.com for some possibilities. They have a sale of cars that run every Saturday, and on the last Saturday of the month, they clear out the back lot of all the ones they couldn't get started (unfortunately they don't bother to list these on line) This auction is located just off of I-81 at the Virginia-West Virginia line. I bought my 740 (and 3 parts cars) there and I've seen nice 240s turn up every now and again. A friend bought one of these not too long ago---a 92 with a broken windshield but otherwise in excellent condition, for $800.

When you have the replacement car, swap over all your upgrades and improvements, then strip the rusty one down to a shell and save the parts for future use. Much less work than dismantling yours far enough to do a proper job of welding in patch panels. Pop rivet repairs can sometimes buy you a few more years, but the structural integrity (very important in a crash) of the car is compromised, and riveting on some sheet metal may keep your feet dry but won't restore it to full strength.