Have a look at what moreil did at http://www.cnczone.com/forums/showthread.php?t=21812.
He used linear bearings from vxb which are $US24.95 for a set of 4
http://www.vxb.com/page/bearings/PROD/12mmLinearMotionSystems/LME12UU
and I see that http://www.marchantdice.com in the UK also have similar available.
Cheers MAL