Price works out when you consider they are produced by hand duebto not being much demand.
Add up the price of a sheet of 1.2mm steel and the time to make them and its about right. Postage is a lot right now tho, probably another 150.

You could find somewhere with a 1.2m or longer finger break (full sheet is 1.2m x 2.4m) and take in a profile of the sill and have them match it. You just do a hundred or so tiny bends to get the curve right. That's how I do it