I wrote an Instructable on converting an old-school "floor pump" (bike pump) to a manual vacuum pump, for a total cost of about $18. (You could actually do it for around $13 with a little more effort.)
The Instructable got picked up as the Hack of the Day on www.hackaday.com a few days later, and got several thousand extra views because of it.
Here's a little video of using the vacuum pump on peeps in a mason jar:
A manual vacuum pump can be used with a small vacuum former for the occasional item formed from thick plastic. You wouldn't want to do it a bunch of times a day, though, unless you want to build up your biceps.
It can also be useful for vacuum pressing wood laminates or vacuum bagging composites. (A similar but smaller pump is used for vacuum bagging small things like skateboards.)
Check out the Instructuable here.