I looked at the photos of the one on Guns International that sold and wasn't completely impressed by the quality of the build. I'm not an expert and don't really follow the modern builders, but his name doesn't ring a bell to me, so I personally wouldn't be interested in paying any sort of premium for the gun at auction. And, for what it's worth, I'm a hack myself, so I'm not suggesting that my work is necessarily any better and maybe the photos were misleading and the gun was nicer than it appeared.
I guess start with the knowledge that with a fairly plain stock and decent components (lock, barrel, triggers, etc.) that you'd have $700 or so in the parts (although you're going to be hard pressed to pick up many Douglas barrels to build a rifle with today although I'm not sure they're worth a premium either). If it's precisely what you need and want and if it blows you away, then pay a bit more than that. If it's nothing special and it's not anything that you're in great need of, try to pick it up only if it's a real bargain (less than the cost of parts). That's just how I would look at it personally, but maybe someone knows the builder better and has some better advice.