I used an old pump from a chest style freezer. The gauge read 32hg while applying a vacuum. Used it many times with no failures.
Unless you just absoutlely have to have the a/c done right now, take your time and get the tools you will need to do it right. Once you got them you will be suprised at how many times you will use them! And at 45-85$ an hour labor they will pay for themselves in the long run.
just my .02$