Keep in mind that if you do indeed order a large quantity of powder you will want to check into shipping by truck. I ordered several hundred pounds of pulldown powder several years ago and had it shipped by motor freight. The rates are much cheaper than UPS/Fedex and there's no hazmat charges.
A small local gunsmith/dealer does this. Orders a skid full of stuff(which gets him a shipping break from the distributer) and has it shipped truck freight, which means no hazmat.
His distributer requires a minimum of 2 8lb containers for powder.