Some of the prices, esp on cab covering upgrades are unbelieveable... But pretty none the less... Like interactive amp porn... Lol 
http://www.sweetwater.com/custom/mesa-boogie/

http://www.sweetwater.com/custom/mesa-boogie/
You are paying for customization, non-standardized process, excess inventory and of course extra profit on extra work. I'm sure you are free to peel off the stock covering and apply the covering of your choice.
Also, covering a shell takes a heck of a lot longer than 8 seconds, if it's a hand process.