Must it be a membrane, or can you flow through a dessicating chamber? Silica Dessicant (Like those "sugar" packets used to keep shoes from getting musty and keeping your beef jerky from growing critters) is relatively cheap and often times reuseable after drying in an oven. I also have a colleague who worked in a cartridge designed to remove water from dry cleaning solvents to recycle the solvent. It worked basically the same as a disposable diaper, super absorbent polymer powder. The product was patented by Proctor and Gamble, but I'm not sure who markets it, or what the trade name is.
ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee