First off, I'm sure it's probably nickel or silver nitride receiver.
Do some research and see what they go for new. It really depends on what a buyer is willing to pay. Keep in mind, it could be tough to sell if you decide it's not for you. We're talking small market for something like that.
Not surprised your not finding any used around. The 28ga is a "niche" gun usually found in O\U's some semi's and few pumps. I would imagine 28ga pumps are made in very limited quantities due to lack of demand.
I'm one of the few at our club that shoots 28ga other than the skeet shooters.
NRA member, DCF&S member, PAFOA member