Not necessarily the cheapest way, but getting a flip-flop hub rear wheel will work. If your chain rings are removable from the crank, take one off. You will either need shorter bolts to put it back together, or grind your bolts shorter.

The spacing of your frame at the rear axle could be a problem. Look for a wheel that is the same or close to your spacing. If your frame is steel, it will bend some with no problem.