I've been researching rollers and trainers as well, and there are a lot of threads on this forum about them. There are some video product reviews on YouTube that may be worth watching as well. I've come to the conclusion that there's nothing like riding your bike outside, and if you want anything close to that, you're spending a lot of money.

Personally, I like the idea of rollers but am hesitant to spend the money unless I can try something out first. Added to that is that all of my bikes are weird sizes, so I need to get out to my freezing garage to measure my bike's wheel base. Also, I'd prefer to use a trainer tire rather than wear out my regular tires (there are different opinions about this too), which are 650c, 20" road, or 26" mtb. LBS carries 26" mtb trainer tires which might be the way to go.

Maybe your best bet is to find something used. And while it may not be ideal, it will at least be good for working on your cardio and pedal stroke, that kind of thing. Save money now, then upgrade later.

I remember reading on one of the threads that someone made a trainer block by wrapping an old phone book in duct tape. Maybe you could stack a couple to get different heights.