Try and get the real mccoy if you can. Picked one up the other day to play with it and a lot of moves are long winded (the way i do it anyway) and if i can't get into the groove or the cube keeps locking (like the cheap ones do) it makes you forget where you are. Considering i hadn't done it since school didn't take long to get back the moves. Everytime i visit i pick up the cube now, although a piece of plastic from inside fell out the other day. Worth having a go...
If you want cheap, I've used this ebay dealer from Hong Kong- http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330249841286
£2.24 delivered. Cant beat the original Rubik branded versions for quality and speed though, but these ones are decent enough cubes for the money.
I used this ebayer because it was cheap postage on a larger order, good for party bags (a different story ) but dealer was fast and reliable and I still have several of them working fine after many months of abuse.
However, I would also recommend paying the extra and buying the Rubik brand. Try your local Woolworths, my one stocks them.
Get practising, the Uk Open is in November .