I would assume that the acrylic bricks would be the more expensive of the two. Acrylic is a fine product with high UV resistance built throughout the product, unlike polycarbonate products which only have a UV resistant surface coating. The company that does the acrylic bricks are called Hylite I think and have been around for quite a while, at Botany. Acrylic sheeting (perspex) that crazes after a while is the cast type acrylic, low grade and low impact resistance.
You have many more choices with the glass though and glass is a more environmentally friendly product. Being in the bathroom you would go for a transluscent or opaque brick. I reccommend the glass brick.
Regards
Adrian See