Just an idea...
If you live near a military base. Go asking around for what they do with their old tires. We turn our old tires in to what is called DRMO, Defense Reutilization Management Office, they inturn will sell those tires in a bid type auction. More times than not, the tires we pull off still have all kinds of life left in them, because we go by a time cycle, not mileage. I know of guys that buy these tires cheap. $100 a set is pretty average, if you only get a year out of them...hell, you only paid $100. A friend of mine, who does construction. Buys our old tires and puts them on his Bobcat (little tractor), he says he gets better traction with our old tires than with brand new bobcat brand tires.
Just an idea, and it might be worth it.