I bought a Tacx one recently from Chain Reaction. It's got a 10 resistance remote thing, folds up pretty small & was only £125. Seems to do the job well, but I have nothing to compare against.
If you get one, I'd also get one of those towel things to stop your bike getting caked in sweat.
I find it pretty boring, unless you are doing a specific type of session – intervals etc. are fine, but if I go on it and think I'm just gonna have a hard, fast ride I get bored & stop fairly quickly.
I bought mine as I wanted something to use when the weather's cak/I get home late from work etc. and I expect to use it more in the winter months.