el-cheapo medela lactina replacement

We recently got a child and needed to rent a breast-pump for a while. the pump was absolutely fantastic and made life soooo much easier (for my wife; now I could also feed the baby at night). However, after a month or so we had to give the pump back. ...and looking at the purchase prices for the same pump nearly gave us heart attacks.
Here is a dirt simple replacement for the really expensive part of the medela lactina and lactina select pumps. You will still need to buy the actual piston set