actually, that’s a ripoff compared to what I paid.
This site has the prices:
http://www.sdplastics.com/komatex.html
I ordered mine through a local plastics supplier, I ordered 10mm, 12mm, and 19mm, I paid about $5-10 more per sheet than the prices quoted above. The supplier I dealt with (if you’re in the LA/San Bernardino Area) was also willing to cut the sheets down to 19x24" which are easy to fit inside the Shapeoko 3. Arguably the biggest failure of the SO3, is that you can’t just stuff something 24x24 into it regardless of cutting area.