You can find them on gunbroker or ebay for that amount or less usually.
It really depends on how badly you want one and how long you can wait and watch for.
I just sold mine to someone on this forum for less than $250.
There is no fixed price on something that is no longer produced, beyond what the market will pay, and mine did three ten day rounds of gunbroker.com, 2 weeks on
www.sturmgewehr.com, and two weeks on Calguns.net, before selling.
I like doing my research and have found some startlingly reasonable buys, that said I have sometimes had to almost give them away when I chose to sell them.
If there was once a hungry second hand market for modelguns, I think it disappeared with the economy.
That said $390 is a fair price if it's really nice condition and you intend to hang onto it.
Jesse.