Avent makes a REALLY awesome manual pump if you are pumping for extra stored supply and not to maintain your milk supply at work full-time. Its extremely comfortable (even moreso than the Medelas) and the handle is ergonomic and doesn't really get your hand tired. Easy to take apart and boil...easy to assemble. Loved it. I actually used it when I worked full-time to maintain my milk supply and it did just fine. But double electrics are easier.
Avent also makes a single and double electric, but I have no experience with either of those.
For double electric, I definitely would have to suggest the Medela, even though its expensive. You can get one through Ebay, but be advised of two things. One, Medela's are not intended for multi-person use, because the system is not "closed." However, I got mine semi-new (used for 3 days by original owner), so I didn't follow that recommendation, myself. Second, Medela's have a working "life" on them. After a certain amount of time, the suction and the pump dies, quite unexpectedly. It could be working the day you pay $100 for it and then die on you the next, if its used. You really have no guarantee with a used pump like that and Medela won't help you.
So, final thoughts. If you're working full-time and plan to breastfeed for the duration, either spend the cash on the good one or rent one (sometimes insurance will cover renting OR buying if you talk to them, first, btw) from the hospital.
If you're just pumping part time or for extra supply in the fridge, I'd just get the $75 Avent Isis manual pump. Loved mine....and it never dies. 