How much does a sheet of foundation weigh

You can buy different thicknesses of wax foundation. Here, a common size runs at around 8 sheets of deep to the lb.

This is quite a bit thicker than if the bees build the comb themselves without foundation, however when bees build comb naturally they do not do it with an intent to build something that can survive a honey extraction machine.

How much wax is foundation saving you or the bees? Anyone's guess. It is said that if thick foundation is used the bees will scrape some of it back to get wax for the cell walls, however in my own observation I haven't really noticed that.

From an old beekeeping book:
Deep, Heavy brood: 6 sheets to a pound
Deep, Medium Brood: 7 sheets to a pound
Deep, Light Brood: 8 sheets to a pound
Deep, Thin Surplus: 10 sheets to a pound
Deep, Extra thin Surplus: 12 sheets per pound

Since the bees will draw foundation more slowly than foundationless, foundation saves you and the bees nothing. Foundation costs them time during a flow. They need somewhere to store honey and the sooner they have a place the more honey they make. Since they will draw foundationless faster they will have somewhere to store the honey more quickly and make more honey than they will with foundation. The most honey, of course, would be from drawn comb as they have somewhere to store the honey now and there is no time delay.