Look for little dusty pet shops that seem to get hidden in little back streets of your local towns, you can pick them up in places like that real cheap sometimes.
One down the road from me had a full kit habistat one on the shelf for so long, and ended up giving it away when someone bought an (equally dusty) viv off him for 50 quid!!
Just been having a mooch as I think I may have got the bug, and thinking of converting one of my spare plastic fish tanks into a starter viv.... possibly considering a young 'un from next years batch??.... not sure yet... however, came across microclimate stuff that seams fairly cheap for small starter stats and so on...... Anyone any knowledge of this make... any good / bad experiences etc??... link: http://www.swiftpetsupplies.co.uk/thermostats-27-c.asp