Standard BB Flange Bearings (ABEC-3):
MF64ZZ are 3mmIDx6mmODx2.5mm thick with flange on one side for ease of installation.
At Helidirect.com, MF64ZZ ABEC-3 bearings are 2.22$ for a 2-pack (1.11 each).http://helidirect.com/abec-3-flange-bearings-2-3x6x25f-mf63zz-p-1201.hdx
Slightly cheaper are the standard (probably ABEC-1) bearings found at AvidRC.com, at 1.00 each:
Also available are Thurst Bearings for 3mm shafting, as used in RC helicopter main blade bearings.
The right model is F3-8M: 3mmIDx8mmODx3.5mm thick.
Available at Helidirect.com for 2.99 (each?):