If you've ever been in the unfortunate predicament of needing a cheap tire, count yourself in the majority. Things happen all the time. Nails appear in tires. Flats suddenly happen. Curbs are hit, which result in a tire that needs to be replaced, but you can get a cheap tire fast, if needed.
Make Sure Your Tire REALLY needs to be replaced and not repaired. When a nail appears in a tire, many tire facilities will tell you that it needs to be replaced right away. When in fact a tire can have a nail removed, plugged and re-inflated.
Opt for a used tire. You don't always need a brand new tire. Sometimes the cheapest tires are those which are lightly used. And have very little tread wear on it. Many off brand store front tire facilities can net you a cheap tire that is lightly used.
Check Ebay for a cheap tire.
Sometimes you can check ebay for a cheap tire. Many people have local hook ups or even have tires from cars they've sold and have no more use for. Before you purchase a tire on ebay consider the shipping costs and the seller reputation. Even better if you can find a local ebay tire dealer to net you a cheap tire.