I'd have to say the PAX Phoenix would fit the bill; low production volumes, unusual design and shoots very accurately "iconic, collectable and deadly accurate". 2nd hand good one should be available between £400 - £500. New ones are priced about the same as a Daystate Huntsman Regal. And I'd probably suggest the Huntsman as a bit of a collectable as well ... but there's hundreds more of them around, but still a game-changer of a classic design.
AA TX200, HFT 500, AS400 .22
Daystate Grand Prix & Mk3
Parker-Hale/PAX Phoenix Mk2: .22 & .177