Greg,

It's easy to make one. The fan is most likely a freebie, if you befriend your local HVAC contractor and talk him into letting you gut a fan out of a boneyard furnace. Try to get a belt drive one if you can, but pretty much any furnace fan will do the trick. With restricted ceiling height, you'll want a smaller one. Or, if you can find an inline ceiling fan with twin blowers that would work really well for you - and none of the premanufactured units are using that. It's like yours is the only basement shop in the world You'd find a twin fan assembly out of a small unit ventilator, or a large bathroom fan. Another thought is to find a fan narrow enough to fit between the trusses or joists, and utilize that space.

Now that you have a fan, hit up the local hardware store for stock sized filters that you like the size of, with a height enough to fit the fan into. Build a box, with filters on the end and sides - as much filter area as you can squeeze in - and wire it up. Presto, cleano. Total net cost about $20.00. The manufactured units use a higher efficiency afterfilter - but running a 30% pleat at low velocity ( as much filter as you can squeeze in...) drastically increases it's efficiency. And they are a lot cheaper to replace.

Position it so that it stirs up the air in your shop, and so that your workspace is in the clean air path. General rules of thumb are 1/3 the way on the long wall, far enough away from the wall for that side intake to be accessable. This stirs the air in a circular pattern...

Dont make the mistake of substituting this for a real dust collection system - DC captures the stuff at the source and contains it, where this gets all the finest dust thats already in the air. But since it is already in the air, it's in your breathing space, and in the house ventilation, and into everywhere else you dont want it. An air filter will help, but dust collection helps more. Ultimately, both are necessary.