We used a second-hand electric breast pump that we found through TradeMe and haven't had any problems. However, before making your decision you should be aware that there is a "small or theoretical" risk that pathogens such as HIV or hepatitis etc may be found in the breast pump.  'second-hand breast pumps-are they safe?' explains this in more detail.

Hand held pumps are much cheaper to purchase new, and may be all that you need? Some people find the handheld ones easier than electric ones too. Guess it also depends on whether you plan to express on the occassional basis or full time. I had planned on breastfeeding but bubs refused to latch and I had a really low milk supply so I expressed for 12 weeks instead (DS had to have formula top-ups too). I wasn't organised and didn't own a breastpump before bubs was born, but rented one of the hospital grade ones for a few weeks from Parentscentre before buying my own.