Smoking in an Apartment/Rental

I'm having a huge issue with my landlord because of the illegal basement apartment smokers. The 2-family townhome was built by the lowest bidder and it shows. When people smoke down there, it's like they're sitting in my livingroom smoking. I can't stand the smell of cigarettes and both my kids have allergies that are intensified by the smoke. The landlord told the tenants it's a non-smoking rental, but likes the money too much to kick them out. So frustrating. Luckily I've got a line on a 3-bedroom stand alone house that should happen before summer.

Anyway, the reason for the rant above is that I priced some of the better air filtration units on the market. It's near impossible to get a good unit for under $600 it seems.