you could probably thread a bmx freewheel on it, unless it's stripped to the point of smoothness. You really only need a few threads to make it thread on.

Maybe try Free Ride over in Point Breeze - they probably have something old and cruddy that will at least work for the time being, and you can volunteer it off if you are literally without funds. if you're willing to sell plasma, Kraynicks has a bunch of the formula / weinmann rear wheels in stock - they were $40 in the winter but the price has probably gone up a bit.