I assume that which you are calling a >downpipe<  might be referred to
as a headpipe??

Good grief...why so expensive??

I have used insulating tape wrap to help keep heat out of the engine
compartment,
when that has been an issue.  Not beautiful, but can solve a problem. Might
give
some marginal protection against corrosion.

There are also places that can do high temperature vitreous enamel coatings.

Crap, for that money I could have had someone make up custom head pipes in
stainless steel or better.