Mig wire is cheap (mig welders are even relatively cheap these days!) if you have the inclination it is doable, but would be a lot of work. Even in my neck of the woods, not hugely populated, and in the rust belt, Sprites and Midgets are still relatively plentiful and cheap. Out on the east coast is certainly rust belt area as well, but there still should be better cars (maybe one you can patch here and there instead of reconstructing the bottom third, and based on what it looks like that is probably what you would have to do) you can turn up with a little looking. I would certainly look at and test, where applicable and if drivable, the engine, tranny, interior, and front suspension. If two out of the four are in good shape worth the price if you are thinking of picking up a Sprite project.