The resale value will depend on a lot of things.
A few are condition, operating hours, spares included, rov type, and demand.
If you had a popular system that has low hours, been maintained well, and has a comprehensive spares package, and you were trying to sell mid summer then you would probably get a very good price for it.
On the other hand if the ROV had been through the ship’s prop then you would probably have to pay some one to take it away.