Ebay is a good place to see what they are going for and what your starting price could be, also there is for N scale the NSC get one of their old mags and check the winning bid prices from the collectors.
If you are trying and not getting anywhere, they are obscure and not worth the effort. They are not gems and worth what they are sold for. Though interesting in history ,practically everything is collectible in model trains. The trick is finding a buyer that sees its value. As a buyer, there are more trains out there then I will ever purchase. It's a matter of what I want next, and what can I afford. In this forum we emphasize the information. In essence you are asking buyers not sellers what it is worth. So keep that in mind.