Well there is a FAS 604 kit up in the sales section right now for £290.

Ad' text here:

FAS604 in very nice clean condition,

Comes with 3 different size balance weights, sight extender, tools, manual, FAS Stickers (unused), FAS embroidered patch (unused) and case (originally Pardini) with combination lock.

Nice complete kit, shoots lovely

£290

Will add pics ASAP
The 604 is a great pistol but look for a Mk2 with the anatomical and adjustable grip. You also want one that has been recently re-sealed and had the felt wiper replaced to ensure good lube distribution internally.
If the seals are degraded, power drops and the pistol fails to punch clean holes at 10m. The pistol I sold on was giving about 370 fps after a reseal. The FAS 6004, the new version has had a poor take-up due to
bad reviews from reported quality issues.