Front brake calipers protrude a LOT, so most 15 inch Ford alloys won't fit without a spacer. 16 inch 12-spoke Scorpio wheels are tested, perfect fit, but don't know about the steel ones...Mondeo steel wheels won't fit, not sure about 16-inch Mondeo alloys. Spokes might lean in too much.
Legends tell of 15-inch Fiesta steel wheel that clears the cossy brakes, but I have not seen such a thing.

Cheapest option might be the 12-spoke Scorpio wheels with worn tires from ebay or somesuch.