Congratulations! The pump that I recommend is Medela double electric pump. It is more expensive but so worth the cost. I used the hospital grade one while in the hospital. I know those can be used by multiple users because they have special barriers in place for that purpose. Those models are the symphony and Lactina. The ones you buy in the store are for single users only even if you purchase new tubing and filters.
I used PJ Comfort's breastpump because my husband's workplace paid for it. It was a hospital grade pump and could be used by multiple users also. It is not the most stylish pump, but worked great. I actually sold mine on Craigslist but only because in the manual it stated "safe for multiple users".
I know some people do buy used ones on-line. I know the chance of something happening because of contamination are very low, but I wasn't willing to take that chance with my newborn.
If you are planning on having more than one kid and breastfeeding them, it is worth it in the long run to buy a new one. They can burn out after a few years of usage so why pay for a used pump twice.
Hope this helps.