I would be inclined to look at the midwest website and see if they have a comparable model. Your kit would be worth a bit less as second hand.
Also look at other manufacturers like Billings, Robbe, Graupner ( I am sure others on this site can suggest more) and look for other comparable kits.
By comparable I mean
- Same size
- same type
- same hull construction e.g. plastic one piece hull with balsa parts of superstruture or all balsa construction.
- parts pre cut or not
- does it come with a bag of metal fittings (for most kits this is an expensive optional extra), door handles, port holes, handrails, stantions etc.
- Does it come with prop/propshaft/motor etc. most kits don't as standard.
Armed with some of this information I would have an idea of what it might fetch, then I would stick it on Ebay. With a reserve of the minimum I would accept. Because in the end it is only worth what people will pay for it.
Do not compare it with static models for value. You have a working model and they do not go for as much money.
For value it is probably better to think of this as an old second hand kit, and not as an antique.
Just some thoughts