Assuming mint, that seems a pretty fair deal. I shoot R stuff on a Leicaflex SL platform, but I recently sold off some, so I'm a little familiar with current pricing.
As with most film stuff, pricing has come down, especially with the bodies.
A mint R6 in box would sell for something like $300-350 on ebay. The 50 Summicron would sell for something like $450-550.
Pricing on that auction site tends to be all over the place, because it seems that most of it is just store inventory, and high prices. Just check the sold listings.