Reply to Best midi controller solely for filter knob?

I have a traktor S2 and would get an S4 if I could afford it, but all I really need is a good dedicated filter. Does anyone know of a good controller with maybe just a few knobs on it? I just want something solid for sweeps. Nothing too expensive. Thanks!

EDIT: I just bidded on a Traktor X1 on ebay. How would that work for filter purposes?