I just found out about your site, and I have to say it's awesome. I passed the link along to the folks at Make and they posted it on their blog of diy coolness.
I was looking at the white plastic cutting board in my kitchen thinking it might be made of noncrappy plastic. By looking around the internets it turns out that cutting boards with the "NSF approved" (not the National Science Foundation nsf.gov, look at nsf.org) are made out of HDPE. Now I think that HDPE isn't as strong as ABS or UHMWPE but it might be a worthwhile option. Since you can get cutting boards almost anywhere.
Edit-
I forgot to mention that you'd probly want to profile the tipspacers with the core since cutting boards are ~1/4" thick.
cheap [?] HDPE for tipspacers
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp