Here's a photo of a 212 cab that had been sitting unfinished in a corner for a year or so -- finally done. I used sling chair fabric as grill cloth, and it came out great. Not sure if sling fabric has been discussed here already or not, but I'll tell my story anyway.
A guy in Florida who owns a bunch of sling fabric sites tried to rip me off, which put me off for a while, but I eventually found a place in Philly (The Southern Company, ask for Sean) who sold me the fabric for less than the Florida dude, even though they don't sell raw fabric normally. It was $35 a yard and 58" wide, though the width probably varies by manufacturer.
The Southern Co. has a long list of patterns and designs with pics on their site. I'd say most are not appropriate for grill cloth, unless you like the look of your grandma's throw pillows, or a beach towel, but there are some really cool ones in there. The pattern I used looks vaguely retro/vintage/deco. Several look like grill cloth from '50s hi-fi speakers.
The stuff is tough as nails and can be stretched really tight. I'm not going to try it, but I'd bet that a kick to the cloth would send the cab flying backwards before my toe damaged a speaker cone.
Since the fabrics are designed to let water through, they also let sound through. When you hold it up, the one I used blocks no more light than a Marshall basket weave.
I hope someone finds this useful.
Cheers!