The thing is.......
1) Regardless of how much it was used... it's still used. So, you can't expect new prices.
2) it's an unusual thing to sell. (very new, and for a specific boat)
Honestly... it's only worth what someone will pay for it... and how long you are willing to sit on it. You could ask $2k... but it could take a year to sell it.
Over the years... one thing I've noticed is that by the time a trailer needs replaced... so does the boat. So... searching for a replacement trailer is very low on the list of most owners.
With that all said... is there a large trailer shop local to you, who may take it on consignment?