There are usually alot of 92 mags for sale on TGT (gun trader). You should be able to pick some up pretty cheap. They are good looking guns, but that is all I know about them.
I have one.
It takes 92 mags.
I love it and I also like interchanging mags with my FS92.
$500 is a great price for that model.
I would jump on it.
92 mags are not that expensive but you might want to consider the Mecgar 20rd mags ~ they are perfect for the CX4.