Ive got a Claud Butler San Remo Racing bike 2004 model that i bought in a clearance sale in 2005 for £300 and nothings ever gone wrong with it except the back wheel spokes went loose and had to retightend under warranty.Ive replaced the plastic pedals with a set of Specialised SPD's and shoes and while biking with your feet permanantly atttached to the pedals seems weird you get used to it very quickly and your speed increaseases as you can pull the pedal up as well as pushing down (if you know what I mean).
By no means am I a expert rider or very quick I could definitley advise a 'racer' if you are going to use it for a specific 'fitness' tool.I use mine for work when I cycle with no problems,however if you want to go off road then youe better off with a mountain bike.
One of the best things to do for a spin session in the gym is one min of light cycling, followed immeadiately by 30 secs sprint cycle on the hardest setting, repeated 10 times back to back, rest for 2 mins, then do it again.
I bought an £80 bike from Halfords and it does me great getting to and from the local gym. I sometimes take it out apart from this but it's generally just used for local travel, great exercise and it makes a nice change to running.
If you want to do cross country which i like most, try out evans cycles, have a look around, depending on how much you have got to spend you can get a nice bike. Around £400 ish you can get i nice spec bike with hyrdo discs, so you can ride in the rain :twisted:, i used to do trials biking still got the bike thats got hydro rims brakes, but these are rubbish for anything apart from trials