Been a bit so I thought I'd bump this up a bit.
What vacuum motors did you use when you built yours? I'm seeing some up on ebay for really cheap that claim new Ametek, single stage, 120,5CFM, 240v at 5.5A. I can get 6 for less then $180.
Is 2 stage important? What other factors need to be considered?
EDIT: Found my plans and the 2 stage 115923 is explicitly called out so single stage is out. That said, these can be found for less than $70 each which isn't bad.