My Jamie's GML S400 GINB cost around £500 after selling the PW stock it came in and buying the very adjustable GINB one here....
He'd switched from his previous BTAS tuned S400 to an EV2 but his scores were dropping so back to what he had before in a slightly different guise and he's back winning comps again.
I tried Evan's AR20 and quite liked it but I couldn't put up with the horrible stock. GINB would make a custom stock for it but need a complete gun for this one, not just a donor stock. Have contacted Walther and Nigel at Brocock but no response from either. Guess they're not interested in a wider market then?
So, at the moment I'd go for a standard S400 2nd hand and put it in something like Jamie's stock if I were you.