Vacuum pumps for chemistry application can be very expensive, and on the lower end, there's good deal that could break, fail, or just not work so well and could easily add up if a replacement is needed. If only the heavy duty components were a bit more multi-purpose and a bit cheaper, perhaps one could justify the purchase for hobby purposes....

Well apparently there's a solution: Vaccon Venturi Vacuum Pump



Obviously this is for those who already own or otherwise have a need for an air compressor, but who doesn't!?

I was also thinking this would go very well with something like fuzzygrowth's DIY condenser for a cheap approach to sublimation or distillation.

Looks nice for filtration, but I wouldn't use homemade equipment when it comes to cleaning solvents etc. for reuse. I read that if you use vacuum for lowering the boiling points of a solvent for refining it and you interrupt the vacuum too abrupt that friction can cause an explosion.

so this one is supposedly $50 - 100 on e.bay; people spend about that much on a GVG or a kg of MHRB.I bought a Gast DOA-P104 on e.bay for $150. this is a heavy-duty diaphragm vacuum/pressure pump used in labs for routine work. it can run for hours on end, and has a overheating safety-mechanism. they're designed to last several years. Welch also makes pumps like these.
Diaphragm pumps aren't very expensive on the 'bay, rotary vanes are (but you don't need fine vac for these applications)

I'm not sure I follow. Certainly there are different degrees of "homemade" which may or may not be suitable for different applications, but this is a storebought device anyway. The distinguishing quality of this device is that it uses the same principles as a water aspirator, using compressed air instead of running water.