Thanks. That heat gun fix is interesting.
Well, since I had good luck at the salvage yard on my first try, I went back a week later. I thought to check the yard for Matrixes, and they had two that had been acquired within a couple of weeks. Didn't have anything in mind except maybe hoping to luck out on some fog lamps. The first Matrix was a mess. The interior was gone, and the inside was filled with the engine. The second was better, and I snagged some toyota cargo nets that were in really good shape, plus a cargo hold cover. I also picked up another high mount brake light. All I had to do was pop it off.
So I wandered back over to the three Vibes I had already looked at, and on the fender of one of them was a set of floor mats. I had seen a rusty corner of one of them peeking out under a pile of metal parts on my earlier visit. So I took the front seat mats, figuring they were worth a shot. The guy at the cash register charged me just for the brake light, $5, and gave me all the other stuff.
Here are the mats, as found:
They perked up a lot after a couple of passes with some OxyClean and a push broom, but the rusty areas were largely unfazed. Some Turtle Wax oxy carpet cleaner did a pretty good job on the rust. I think I can live with them.