Help! Best breast pump for full time workingmom?

Hello! I am going back to work soon and will need a better electric breast pump than what I have (Ameda purely yours) but I am not sure which is best and most affordable. I've heard Medela is good but they are so expensive. Any suggestions on where to find an affordable one? And the best kind? I have to pump at work and will not be able to feed my son at all during the day from the breast so I need a pump to really promote production. Thanks in advance!