Man is there are lot of misinformation here...
Instead of sorting it all out....
Lets just say this. If you have a local plastics shop, you can get CELL CAST acrylic for the same price HD is selling the EXTRUDED junk for. Can you use the HD stuff? Sure it's extruded, will absorb water to an extent and is harder to machine and is much more prone to crazing. Cast products are prefered.
Lexan... not worth the trouble. There are a dozen reasons not to use it. Cooluser, the products you mention are UV stabilized and very expensive to say the least.