As others said, probably a used tire on eBay. They come and go fast so you probably have to search for a few weeks. Otherwise if you can't be bothered, I'd just get a set at Costco. At least they offer a 5 year road hazard and if they're practically new, the next time you have a flat that can't be repaired, you'd probably only be paying for 3 tires instead of 4.
Did you do the flat tire bit?
Did you do the flat tire bit?