I dont know where to get a cheap one because this kind of pharmacy things usually comes with standard price ..wont be anyway cheaper unless u have contact inside the factory or sale related for the particular product.

I got some idea, u mod the house hold suction hand pump ..
it is same concept but bigger suction and capacity ..

the only thing should be careful is the 3 ways valves, make sure no contamination ...no lubrication fluid/dirts from the hand pump ...can put a filter to be safe.



OR

buy a 2nd hand one, because usually the baby is big enough we feed commercial milk already, so get from those ex-breastfed mom.