I just recently updated to an Ultrex and I'm selling my Fortrex. It's a Minn Kota Fortrex 24 volt, 52" and 80lbs thrust, I bought it for $1,359 any suggestions on what I should sale it for? Only had it one year.

2D sonar built in to trolling motor on bottom.

How old is the Fortrex?

Just guessing here, but likely sale around $750. Its worth at least that to someone wanting 24V80# & 52" shaft.

It's a year old.

With the popularity of the ultrex I think the used fortrex prices will take a big hit.

You're going to take a hit if you sell it now. Yes, it's worth $800. range, however, since the warranty is only to the original purchaser, it is selling with no warranty, even though it's a year old. Many that are in the market for that trollingmotor will spend the extra $$'s to get the "new" one with warranty. This means to sell yours, you're going to have to get it down to where someone is willing to exchange the warranty for the price savings.
I know you don't want to hear it, but I see it daily.
John