I've got two vac pumps that I've used for a very long time now - bought a Thomas Riechly (sp?) wobbling piston type pump on ebay for less than $35 about 15 years ago. If I remember correctly, they are often used to aerate ponds - continuous duty. It develops 26 inHG and has consistently done everything I need. I have no idea of the CFM, but it handled vac chucking on a Jet 1642 without issues. Rebuild kit was available on line a few years ago. Replacing the startup capacitor has been the only fix to date. I upgraded lathes to an AB, and when I had an opportunity to get a Gast rotary vane pump new, in the box from an outfit that was liquidating surplus hospital equipment stores on ebay for less than $100 with shipping, I hopped on it. Both have been working ever since - the Gast handles vac chucking on the lathe and the Thomas easily handles duty on a WoodCut carving stand that takes the same vac chucks. Both have been virtually trouble-free. The Thomas is a joy to use with the carving stand - very quiet.
I've seen vac pumps available as diaphram based, wobbling piston types, rotary vane types and oiled or oil less - I wouldn't want to deal with the issues of an oiled pump in my shop, that leaves the diaphram style, the wobbling piston type and the rotary vane style - any of them work well in the application. Look around, there are still deals available and these things respond very well to a simple rebuild - most are made for continuous duty cycles.