Are you willing to buy used or reburbished flash drives?
Because if you are you can get great deals on older models.
I guess it really depends on how much storage you need since the newer models typically have 64 or 128 GB of storage.
Older models like 4GB and 8GB can be found online cheaply.
I found a Lexar JumpDrive Traveler 256MB USB 2.0 Flash Drive for 1.99 online at Geeks.com.
They had many other deals like this for smaller sized flash drives.
Check out that site and you should find some great cheap flash drives.