There's a few considerations you need to take into account when pondering a trainer.

If you have never been on one, and are unsure whether you'll stick with it, get a cheapie that's well rated. You'll hate to throw a $400 trainer in the basement never to be used because it turns out you hate indoor spinning. (We all do, to some extent, but the rewards we reap outside later keep us going.)

True wind trainers, with fan blades, are noisy but cheap.

Magnet trainers are nice, but can skip and feel rough.

Fluid trainers most realistically represent differences you experience outside with regards to acceleration and speed. The effort you need to accelerate up 5 mph is similar outside and on a fluid trainer or rollers, but less similar on other trainers. CycleOps has a good track record and has some nice accessories (front wheel stand, bike mat -- which is a MUST if you're like my hubby and myself who sweat ferociously and leave puddles on the floor) and will set you back $200 depending on the model.

Best bet? Buy one used from someone who shelled out and never used theirs!