you guys need to be moving more of a volume of air through the filters. Computer fans and the like aren't gonna cut it in my humble opinion. As stated before, you have a perfectly good option in this product :
http://www.caswellplating.com/aids/cyclone/bldc1500.htm (which can do double duty for your sandblaster as well. Remember the theory of no "one trick pony" in the shop) or if you just wanted a filter for powder only, a shop vac would be best. You can pick up a viable one at any reatil outlet and get the "fine" filter for under 75 bucks. Remember.... these are your lungs we're talking about here,folks. I for one wouldn't trust them to a computer fan or anything of the sort. (side note... a furnace filter won't be helping you any as the smaller particles will flow right through it, car filters are too restrictive unless the surface area is a LOT bigger. Like 20 flat car filters bigger). Like I said before.... the booth and what not, I have no problems with any variation out there. The exhaust on the booth? Wayyyy different story. I'd seriously re-consider agains make-shift fans and so forth and just go out and get the equipment that's "meant" to handle the problem first hand. Otherwise you'll learn soon enough that you'll be out buying it anyways. Not only will your parts turn out better in the long run... but all that time saved cleaning up powder from everywhere and going in a direction that may not work in the first place will be avoided. (more time to get your buddy to help you sandblast,lol). Just my humble opinion on the whole matter,guys. Take it for what it's worth, I suppose...... Russ