I've personally never used a carbon shelf so I can't address that part of your question but I have heard and read that carbon shelves work well. I had two custom black acrylic top shelves made for two of my Billy Bags racks that I'm happy with and work well.
As you stated both carbon and acrylic are pricey! Depending on the dementions of the shelves and how thick they can be you might also want to consider custom maple shelving made independently or see if a company like Mapleshade can have some built.
As you stated both carbon and acrylic are pricey! Depending on the dementions of the shelves and how thick they can be you might also want to consider custom maple shelving made independently or see if a company like Mapleshade can have some built.