These days, maybe a little steep, but not far off.
There used to be a seller on ebay who churned out refurbed TTRS calipers for 350. He now only seems to offer the refurb service itself. The calipers seemed more common second hand a year or so ago, too.
So really, supply has affected demand, and hence price. 500 isn't that bad. I mean, show me where you can get a refurbed pair for 350 today.....?