I wouldn't recommend buying a used one. You don't know how many cigars were cut with one, and it could be dull. I'd however recommend anything made by Xikar. They are backed my a no-questions-asked warranty.
Depends on the type of cigar cutter that you are going for...
If you are looking for something reliable, long lasting and in budget I suggest Xikar Titanium Finish Cigar Cutter . As everyone xikar quality is top notch.
Or if you want something very cheap, good quality and simple then you can go for Alaska bear, I have 10 of them just lying around for emergency purposes.