I'm in Canada, but even in our market, it looks like a fair / low price range to me.
If I saw it I would also probably offer $1000 (only because that's what it's worth to me ... which is a different matter than what it might actually be worth). It has extras (dump, gearing, and tool box, winch ?, battery, loading ramps etc), so I certainly think your price is reasonable. When you say 18 ft, that is the box / deck length correct ? it looks to be 6 ft wide. If I was buying, the axle details would be important.
As a seller, consider what is it worth to you - you bought it as an extra with the tractor, so there is some value there - don't give it away.
If it takes too long to sell, maybe consider the equipment auctions in your area - min bid $1000 ?
Another thought is to make it a charity donation and simply get a donation receipt for the value of the trailer (my wife volunteers at our very busy Thrift Store and I see what they use for equipment).
You seem like a reasonable person, and I think you should have no trouble selling it.
All the best.