here is my idea for a cheap and simple dust filter. Use an exhaust fan(impeller
type) to suck the dust laden air, then blow it through a bucket of water. The idea is to force the dirty air through water so that the particles will get stuck in the water. To better increase contact of air with water, maybe diffuse the air through many smaller hoses in the water, instead of just one big hose. I havent tried making this but i would like to hear from you if this will work or not.