It's probably not worth buying beans purely to make your own extract; buy what you need to bake with and then reuse them in a bottle of alcohol for extract you can use or give away as holiday gifts.
Click through for a few good sources of vanilla beans in bulk.
• eBay: The last time we bought beans in bulk we did it through eBay. We bought 35 Tahitenses variety beans for $2.25. With shipping at $5.50 the final price made us feel like we were either getting away with something illegal, or about to be duped.
But the beans arrived promptly, and they were plump and fragrant and wonderful for baking. They were slightly dryer than the more expensive fresh ones we find at Whole Foods, but at 22 cents a bean we weren't complaining.
• Saffron Imports: Recommended by Melissa at The Traveler's Lunchbox in her original post on vanilla extract. Here a pound of vanilla beans will run you $19.95 to $28.95.
(Image credit: The Vanilla Shop)