I have seen Shizo Saburo tamahagane from the same seller for ~ the price you payed for it, but Iwasakis definitely go for a lot more.
Here's the description. From what I have gathered from someone I know here it's an old stock Kamisori made a while ago. I have a tamahagane coming to me actually ( not for 50000 yen either. But this one was unique and as I will probably not use the tamahagane to shave this one is cheaper than the new ones so I was thinking about it and was wondering if anyone had an old stock to compare it to. If not I'll try the BST to see if I can trade for it. It might not be the best shaver to some but its beautiful.