Hopsdirect.com has by far the best prices. The only downside is that they sell by the pound, not the ounce. They also charge for shipping (standard UPS rates. From the farm in Mabton, WA it cost me about $9 to ship five pounds to Olympia, WA on the other side of the state). They have a great selection of both whole hop flowers and pellets. The only problem I have with them is that they do not sell Simcoe, which is one of my favorite varieties. Hopsdirect also sells rhizomes if you want to grow your own hops.
freshops.com sells by 2 ounce increments and does not charge for shipping. They also have a larger selection of varieties but only sell whole hop flowers, not pellets. They have Simcoe whole hop flowers. They also sell rhizomes.
Nikobrew.com has a good selection of hop pellets and charges a flat rate of $5. They have simcoe pellets.
Overall, my advice is to pick three varieties of hops you think you will use the most, buy a pound of each from hopsdirect, then vacuum seal them in oxygen barrier bags in the one or two ounce increments and put them in a freezer, preferably one that won't be opened very often.
It may seem like a lot of hops, but you'll save a lot of money and always have plenty of hops on hand.