Trailboss has a good idea with the exhaust fan. When I had a darkroom, I had a 300CFM exhaust hood over the fixer and toner trays. I could smoke a cigar in there and not smell it in the house. The downside is that you are exhausting conditioned air and pulling in air from outdoors, so your heating bill will rake a whack.
HEPA works well, but you need a sufficient CFM/air changer per hour for it to be effective. Woodworking supply companies like Grizzly have HEPA units that will work well for this, with the addition of a charcoal filter layer, for a lot less than a flimsy consumer unit from Best Buy.
An Ozone generator will work very well for eliminating odor, but inhaling ozone is quite bad for your lungs. Ozone (O3) has a fairly short half-life, before it degrades back to O2, so if you can leave the room and switch on the ozone, then you are in business. Better yet, turn on the exhaust fan once the smoke odor is gone.
Best best would be to move to the garage, and run a small exhaust fan out there.