"What's it worth?" That's a question I got asked several times a day when I ran the gun shop... and it isn't easy to answer. First, the question kind of assumes that the value of the cash involved is a universal constant. It isn't. A dollar to me is worth considerably more to me than it is to somebody who has a gajillion dollars.
If you are looking for a gun exactly like that, if you have sufficient funds to buy it without having to hock your guns, get rid of the cats and sell pictures of your wife's (.Y.) on the Internet, then maybe it is worth that to you, but not to me. I would want it in 16 gauge, for one thing, and even if it was a 16 gauge, that's a couple year's worth of saving for me, so no deposits to my Roth IRA and no other toys for two years.
The true market value of anything is whatever the market will pay for it. Watch the item and see what it sells for. Then you will know the answer to the question of "What's it worth." Otherwise, buy it. If you buy it, it was worth what they were asking, nicht wahr?