+1 on a salvage motor from a Ford Panther series (Crown Vic, Grand Marquis, Town Car). However, make sure it's a 2001+ in order to get a PI motor to be used whole.
The motor in my 2000 GT was acquired via LKQ. Low 30K mile motor from a 2003 Grand Marquis for $800.
Tip. Salvage yards are required by law to retain the VIN numbers from where the part comes from. Get a CarFax report on the donor VIN number for any salvage yard motor under consideration. This will give the mileage when the car was totaled and a way to check the 'honesty" of the salvage operator.
Tip. avoid any motor from a Police vehicle. Why? Because mileage is a poor indication of wear since Police vehicles spend soooo much time idling.