What is important is repeatabilty, so it should always be those 40ml/ 4cm pushing and pulling.
If there is some degree of precision required, then a total low tech might not meet the specs. Just looking at the Martin P. jones parts catalog, they have a 60cc "irrigation" syringe for $.95 (with $9.95 s&h 
). Sometimes the big syringes are used to feed infants and animals too.