From McMasterCarr: (1/4" ID X 1/2" OD X 1/8" thick)

Viton O-ring are $5.46 for pack of 25 (PN# 9464K118)

and Buna-N O-rings are $4.00 for pack of 100 (PN# 9452K183)

There are other materials too, just search for "O-ring" on thier website......... http://www.mcmaster.com/

Not sure about shipping, I think they are reasonable? Usually UPS ground.
We have McMasterCarr locally here in Atlanta. So, I can go pick them up myself.