It really depends on your comfort level, and how often you're going to need to pump. I'm a SAHM, so I only needed to pump occasionally (to increase my supply and on the rare occassion DS and I were separated). I borrowed a Medela PIS from a family member, and it worked fine.
If I were working outside the home, I probably would have purchased a new pump (or rented a hospital pump, especially if I had to exclusively pump).
Stacy
Wife to K
Mommy to A (5) and twins E & S (1.5)
The biggest mistake I made is the one that most of us make...I did not live in the moment enough. I wish I had not been in such a hurry to get on to the next thing: dinner, bath, book bed. I wish I had treasured the doing a little more and the getting it done a little less. - Anna Quindlen