C.C.
I used a Medela hospital-quality pump that I borrowed from a friend. I never tried the Gerber pump, but I did try the Avent hand pump and couldn't even get an ounce out! But with the Medela pump I was able to get 8 ounces in under 10 minutes. So the kind of pump you use can make a big difference. Ask around and see if anybody you know (with toddlers or preschoolers) has a pump they aren't using. All the parts that touch the milk or your body are dishwasher-safe so it is ok to rent or share pumps. Also, sometimes hospitals will have a pump rental program with payments on a sliding scale depending on what you can afford, so that's an option too.
But it's also fine to give your baby formula when you need to! The formulas they have now are very good, and your baby will do fine on that too. (The only drawback is, it costs more than breast milk! =)
Congratulations on your baby, and good luck with school and work!