That's about the going rate. Last time I saw one, 50mm in EX+ or something like that was $375, I think. Price wise, you can do a lot better if you can settle with 65mm. I bought a K/L version but C version is quite a bit less.
I buy used stuff from KEH, Adorama, and B&H. They are all equally good when it comes to accepting returns for whatever reason. I received duds and excellent stuff from all 3, so I keep watch on all 3.