A lot of that will depend on condition.
The basic fomula is to look at MSRP of the gun as new, subtract $100-$150 to find average retail, then subtract another $100-$175 for used. More if the gun has more wear and tear etc.
Has an MSRP: $467.00
Average retail would be around $317.00 (Google Shopping shows two prices of $319-$329)
Take into account used factor, probably around $150-$217