I'm still here! I don't post much, but I lurk in the background.
I think I paid $600 for mine and I recently
sold it for $1000. That was with new
tires and hubcaps, new
paint, new floor, new interior
LED lights, and new LED running and brake
lights. It really depends on your market. I live in western Washington State why dry and lockable utility trailers can fetch a premium.
Given what new enclosed and lockable trailers sell for, I think a price in the $600-$1500 range is fair depending on the condition of your trailer and your market.