If you have an extra 5 gallon bucket and a length of hose laying around, this is by far the cheapest solution to add a cyclone pre-filter to your shop vac.  I initially had some issues getting the lid to stay on the bucket, but I had great results after adding some weather stripping under the rim, and aligning the lid such that when the bucket handle is up, it's pushing down on the lid.  I also dedicated a piece of hose to connect this to my shop vac, which I then sealed in place with silicone.  I've not noticed a drop in suction, and I get a lot of material dropping into the bucket instead of the vacuum.