I built a little gym in my basement a while ago. There are no windows, no real ventilation and it's finished. The air is stale and musty (not HORRIBLE, but enough that I don't like doing cardio down there, I feel weird about breathing the air in). I have a dehumidifier down there and 2 "air purifiers", I put it in quotes because they seem to work more like fans that circulate the musty air than air purifiers. For those of you with basement gyms, what do you do to clean and freshen the air? I don't have money to go buy some crazy system, maybe some unit that's under $200 or so if it comes to that. Any advice is appreciated.