Hi Varivoo! Welcome to the forums!!! 
I guess it depends on how much rust there is. I assume you are talking about rust on the rollers? Good old WD 40 will may help and and a very light coat will keep it from future rust. Super fine steel wool or a kitchen scrubbing pad may remove rust but be careful not to mar the smooth surface. If you have a lot of rust a rust remover product like Naval Jelly may be required. Be warned that deep rust pockets mean you will have a pitted roller.
Most mills have stainless rollers which shouldn't rust. If your is not stainless it might not be as much of a bargain as you thought. Keeping your mill dry is the key to avoiding rust in the future, A very light coating of thin oil like WD 40 helps. (I've been told that WD stands for Water Displacement, as it if is intended to drive out water and leave a very fine oily surface.) The amount of oil left on your pieces should be easily removed with warm soapy water or sudsy ammonia and warm water.
Hope that helps!