We just bought some today from
www.stagespot.com
15.25 a roll but we got free shipping..
We did buy 3 rolls of gray, and a roll each of yellow, red and electric blue...
hope that helps...
(I checked the site mentioned earlier and for what we bought (6 rolls) it was almost $19 cheaper at Stagespot because of the free standard shipping. )
One note... keep this tape away from students unless you want it to disappear.... they all seem to think it is duct tape and like to use it for non-field uses... buy cheap duct tape for them to use...save some money...