Not as cheap as MSE, but it does a fairly thorough job. I've used the free version before and quite liked it.
Pro version adds realtime scanning, auto updating + heuristics to attempt to remove zero day vulns.
FAQ: Does Malwarebytes Anti-Malware replace antivirus software?
Answer: No.
http://helpdesk.malwarebytes.org/entries/20818081-does-malwa…
It is pretty much the best of the Spyware Protection options out there. It can be a little invasive and clash with other software but it'll deal with the nasties the others ignore or pretend to clean. It's saved my bacon more than once.
I've only used the free version but the Pro version at 1/2 price looks pretty tempting. I just wish one license allowed multiple uses :)