Prices vary. An item is worth exactly what someone else is willing to pay for it. A lot depends on how quickly you want to sell, & how bad the buyer wants it. If it is (truely) a rare item... Caution: some sellers think everything they have is rare, problem is they are not so. If it is truely rare, then a buyer who really wants it would be willing to pay more.

Then there is the matter of condition. You say it is in excellant condition now. The trick is to use it & enjoy it, but minimizing the wear & keeping bad things like rust away. Original factory items like grips add value to a collector, & even if you use other grips the correct grips should stay with the gun. As others have stated, diamond targets are too early for your gun. You could buy the correct ones & sell the diamonds for a profit.

Model 28's are not rare. Still, there is a good market. You did get a great deal.

Nice find. We're all jealous!
Russ