I have a used Michelin Pilot Sport tire that I had kept as a spare in case of a flat. I no longer need it since buying a set of winter wheels and tires. There are no patches or plugs and holds air without issue. The inside of the tread measures at 4.5/32 and the edges are at about 5/32. So figure about 45% of it's tread life left.

~$75 via Paypal or local pickup in Scranton, PA