My 2005 and several other years of Bigfoots used hdpe, hmwpe is extra cost and not needed. By the looks of your picture Bigfoot must have used a plastic product similar to hdpe (hdpe won't crack like that), I don't remember the name of the plastic in the picture, some hardware stores carry it, sort of a poor man's hdpe, Bigfoot must have used it for some time, it's half the price and with age will get brittle and crack like the product in your picture.
The product that you linked to is what my Bigfoot came with from factory 1/8 thick, In Canada most Lowes or Home depots would carry it for approx. 40$ for 4x8 sheet. In US not sure?