If you contact
Applied Industrial or
Motion Industries and ask them for an inexpesive ball bearing that has a 1/2" bore with a flange, they should be able to find you one that costs at $6-10 each. Ask to have them look for an "import" or a lower quality bearing.
When you ask for any general "import", you are asking for a generic bearing that is cheaply made by just any manufacturer. Of course, many bearing manufacturers import their products to the US, but you need to specify their part # and manufacturer name. In your case, any generic "import" will work. 1/2" bearings can handle a high amount of radial force and a gearbox application in FIRST usually does not come close to overloading a 1/2" id bearing.
The more expensive bearings ($15-20 each) will spin easier since the bearing race is machined more precicely (ground), but an import will work OK.
Good luck,
Andy B.