That's a common belief but not true:
http://www.epa.gov/Ozone/title6/609/wantknow.html#q10

Everything I've read about those cheap vacuum pumps has said to stay away from them, the only thing they are good for is wearing out an air compressor. A good A/C vacuum pump is generally pretty expensive ($200+) but you can sometimes find them cheaper in a pawn shop.

If it's only empty because you accidentally opened it up and you just need to get it vacuumed and refilled then take it to a Jiffy-Lube type of place and get it done.

The tools to work on an A/C system aren't cheap but they will pay for themselves after a couple of repairs.

Also Sam's Club has great prices on R134a, I think a case of cans was $36 last time I looked.

 

been using one of those cheap devices for over 20 years- never had a problem and never wore out a compressor.