Valuing Used Show Equipment

I am trying to buy the following items and the current owner asked me to figure out what they are worth and make him an offer.  Before I do that, I want to make sure it is fair for both of us.

2003 Featherlite 24' aluminum stock trailer.  2 cut gates with 1/2 slide door, rear full swing door with slide, interior lights and ties down the side of the trailer.  One owner, paid $11,000 new.  Good condition

Sullivans 8' Aluminum Chute

(2)Sullivans Aluminum panels

(2) Sullivans fans with panel mounts

Any help on values or resources to find values would be greatly appreciated!

As far as the show equipment I always just sold it for half of what it was priced at new, it was all taken care of but had some hours/use on it. The trailer first check the tires, look for the mfg date, how old are they, they may look fine but if their over 8 years you will definitely have to replace them. Is it an aluminum floor or wood, if wood what condition is it in. if it is all in good condition it is probably worth what they paid for it, Looking at what they are selling for his purchase price would be a bargain.
Chute: $500 (894.50 new)
panels: $350 for both (299.99 New)
Fans: $250 for both (New 252.500 each) Check fans blades, cords,and cage if anything needs replaced knock 50 off

$11,500 - $12,100 For everything

Not sure if this helps or not but the farm I was working for sold all of their show stuff in the fall. It was all three years old or newer and very well taken care of. We valued most of it at 70% of the new price. We didn’t have any trouble selling it and I was happy to buy a few things for that price.