How much should a torque converter replacement cost?

I have a 2004 Explorer V8 4X4 that needs a new torque converter and front seal.

I was quoted 1600 at a Ford dealership. How much should I reasonably expect to pay at a non-dealer mechanic, and what merit does the dealer have when they say aftermarket torque converters won't last long? My first thought was that the Ford one only lasted 50,000 miles so do I really want another one just like it?

It was leaking transmission fluid and making a grinding noise, the dealer said the torque converter was out of alignment and caused the seal to leak.