I bought several Hexar AF (all 'Original Black' Hexar's with HX-14 flash unit) over the last 25 years.
Bought my first in 1994 - traded it a few years later for a Contax 137ma SLR - bought another one in 1998 (about 700,- Euros from a German camera store) - lost it in a gondola lift in the Swiss Alps near Grindelwald -
bought my third one in 2002 (about 500,- Euros + VAT + shipping coming from Japan / ebay) - lost it during the break up of a relationship.
Two years ago I got my fourth Hexar AF (600,- Euros + VAT + shipping coming from Japan / ebay).
I think those Hexar's have a stable value.
--
$600 + shipping should be a reasonable price for a Hexar AF in excellent condition.
$600 is too high unless you have box and flash and camera is mint.
Prices for listings on ebay are simply that...just prices.
Selling prices is another thing.
I don't think I'd go above $495. I buy and sell frequently on ebay and the Hexars
are Cam's I follow. They don't sell for the big prices you are seeing...the just remain on Ebay.