You wont be getting a decent full sus until you get to the £800 mark and it still wont be light.
That's certainly true at RRP, but there are deals available.
Pauls cycles in Norwich specialise in NOS bikes, and have a few bargains. If it was me, I'd look at the Giant Anthem/Trance/Reign models on that list (I rode a Trance 2 when the model was new, and reckoned it was worth the £1750 RRP, then). Also the Kona Kikapu Deluxe 2006 looks good (if you're a giant - otherwise it's the 2007).
Winstanleys also offer old-stock bikes at knock-down prices.
Having said that, if you're primarily a Road Cyclist, I'd suggest you seriously consider a hardtail - less to go wrong, lighter, and more like what you're used to. Pedalling a FS efficiently takes a very specific technique, which may or may not come naturally.