You can get resistance units to go along with rollers. And, as others have mentioned, you can also add a fork stabilizer -- as far as I know, only Krietler offers this attachment. [Edit: Nope, it looks like CycleOps and Minoura make them too.]

I have a set of Kreitler rollers with 3" drums (Poly-lite) and the wind resistance unit. You can vary the resistance by adjusting the wind unit. This has the added benefit of providing a cooling breeze while you're toiling away indoors. The 3" drums and the wind unit provide more than enought resistance for me while grinding away on a 48x16 gear. You can also stand up and sprint, but this tends to unweight the rear tire, which causes it to slip on the drums -- kind of like sprinting on ice. It will, however, definately improve your balance.

The caveat is that these aren't cheap. Kreitlers will run about $280, and the wind unit is another $160. The fork stand will run you another $90. There are other brands out there for half the price, but Kreitler is kind of the Chris King of rollers -- buy it once, buy it right.

But since you're looking for "super cheap", you may be better served by a trainer. You can get a really hard, focused workout with a trainer, but my god are they boring!