From the CL add it is difficult to determine which model, but this '81 World Sport looks about right.

http://www.trfindley.com/flschwinn_1...0/1982_13.html

If so, the frame is on the heavy side, but would convert to a beater SS/FG nicely. But your concern about the conversion price is well founded. New aluminum rimmed wheels to replace the steel rimmed originals would set you back about $100-200. New brake pads, cables, tires, and bar tape, another $50-75. If you can live with that saddle, OK, but most of us would find it to be a real PITA (literally).

So, by all means you are nearly at $400, so think carefully before you buy the World Sport. Best of luck.