shipping a manifold

Packed well in the proper sized box. UPS and FedX will cost $35-45. Probably cheaper through USPS. The post Office used to have a flat rate "game box" that a normal manifold would fin in but they dropped that one. Probably too many shippers abusing the size. .
No way in hell at that cost.
You are severely undercutting what it's going to cost in sending out a cast iron manifold.
Depending on distance, and total weight of the package.
I know, as i regularly send out brake and suspension parts, USPS, and FEDEX, and it ain't cheap anymore, in this modern day and age.