All 6906 are aluminum frame.
The "market price" of anything is what someone is willing to pay for it. All you can do is compare what others have been willing to pay for a similar item and decide #1) if you can get it for that price or cheaper, and #2) if not, are you willing to pay the higher price bacause it's something you really want?. You would not be the first to pay that much, or the last. It sounds a bit high for my taste. Maybe way high for some but there may be someone out there willing to offer the seller more to get it away from you! I just gave $375 for a used one that came with a holster and ten 12-round magazines. Some would be willing to pay more than that. Others have been lucky enough to pay less.
I would think many people who own more than a few guns have at least one or two that someone thinks they overpaid for. I recently paid what some may say was too high a price for an SKS. Sure, a year ago I could have gotten it for $100 less, but a year ago I had no interest in owning one.
If that's the gun you want and it's available right now and you can afford it right now, well then....
How bad do you want it?