How much edible glitter would it take to cover a 4", 6", 8", 10" and 12" round cakes? 

This is the look from the drum set they want copied onto all of the tiers.  Lots of silver glitter.

AWow, ummm, a lot. The ones I have are like 5g. But I still just use for accent pieces personally.

Same here, only for accents.

I found 4 oz jars for sale, I just have no idea how many to get.

Yes, alot! I would color the icing a darkish gray then add the edible glitter. This would help you to use less. Just remember, no disco dust!!

Oh yes, I made sure it was the edible glitter and not the disco dust :)

Wowsers, that is a LOT of glitter people would be eating! I know it's edible, but still....maybe just not my thing :)

Not my thing either.  I just can't get past how it would "feel" as you chew. 

Maybe you could convince them to use a pearl sheen instead? I also wouldn't want to eat all that glitter.

AEven though it's considered edible I wouldn't think it would be healthy, perhaps you could explain that to your customer as well as the price for 80-100 bottles of glitter. Not everything can be accomplished (and I don't say that lightly).

Or you could use sanding sugar, you could color that or gold gelatin setup and chopped finely-that would give you the closest look without spending a fortune! I just googled homemade glitter and the gelatin looked like a hologram, you'd just need to color differently.

Very good alternative ideas!  Thanks for the inputs.