I'm no expert, but my impression is that a good hammer double rifle in .500BPE starts at perhaps US$9,500. That would be for one with little or no original finish, and probably re-finished in the past. A gray gun with usable bores and wood. An example I would point to is an H&H being currently offered by Westley Richards for US$10k:

You will notice that the stock of this rifle is broken and repaired just behind the head, to the left of the top tang. Also notice this is a "Plain Jane". Little or no engraving adorns it. Here is a closeup from the WR website:

That should give you a feeling for what US$10k will buy.

It's all uphill from there, in terms of price and condition. I think I can assure you that you will not find a good original condition rifle at a yard sale price.

My heart also skips a beat when I handle a vintage hammer double rifle. Somehow I can't warm up very much to the poor examples that have been "gunsmithed" to death. I want good original condition with no refinish. That's a costly proposition. Here's a pic of my Purdey .500BPE, which has been shown on this site before:

This rifle was delivered in 1894. It remains in fine original condition throughout, still residing in its original oak and leather case.

Please forgive the barrel distortion in this photo. The case is straight and only appears bowed because of the aspect of the shot.

Here's a composite photo of the case label and the charge card:

I think it is interesting to see the black powder warning stamped on these labels. Here at the dawn of the nitro era Purdey was worried that someone might put a .500NE in the chambers. The same warning is engraved on the bottom rib under the forend.

In my opinion you cannot go wrong buying quality and condition. You pay more, but you get much more in the bargain. As the years go by that choice will repay many times over.

Curl