My cost on high grade Cell Cast 4'x8' sheet is:
1/4" $118.40
3/8" $177.92
1/2" $243.52
3/4" $388.16
1" $526.08

If you dont buy much acrylic you could pay a bit more than that, and if you buy alot of acrylic, you could pay less than that, whatever you do, dont go to Industrial Plastics unless you want to remortgage your house....

multiply those prices by 2 and thats about what IPP charges for low grade extruded acrylic sheet