In my experience a torque converter has never gone bad. If the TC is a locking-type, then a slipping TC clutch would be a clue that failure was imminent. Running in 3rd or OD, slippage can be detected by an increase in rpm when light to medium throttle is applied.....but slippage can also be attributed to low system fluid pressure in the tranny.
Changing out the TC is no major job outside of the need to back the transmission away from the engine far enough to get access and room to remove the TC.
The price of a TC can be found at any Genuine Ford Parts site. Just get online to one and start the drill-down. I'd recommend against aftermarket converters unless they're from outfits such as TCI or other reputable tranny rebuilders.