I have finches and budgies, and buy larger bags of seeds and freeze briefly to make sure there are no moths/larvae. I store seed in Rubbermaid commercial two and five gallon clear polycarbonate freezable boxes with lids (available online, they are made mostly for the restaurant business).
One product where I've found that it a really a saving to buy in bulk are the five pound boxes of millet sprays.
If you only have a few birds you can always find a friend or two and buy and divide up a box. The birds love millet spay and it is way cheaper to buy it by the box.