This Rimmel Match Perfection face loose powder is an amazing if not the best dupe I've found for the Laura Mercier loose setting powder. I've used it for setting makeup and baking under the eye concealer and it has not failed me. It performs almost identically as the Laura Mercier one and it is almost one tenth of the price. I found it at Walmart for $4.99
I've tried the Boots No 7 loose powder, a couple of NYX, Too Faced among others and I've found this one to be the closest to the Laura Mercier one.
Have you tried it?