Nidhg00670000 posted:

Welding cast iron is a bitch. To do it correctly you need to pre-heat the whole manifold since cast iron isn't very ductile, it cracks easily due to thermal stresses when rapidly heated or cooled. If you do it incorrectly the carbon (cast iron has a high carbon content) might also migrate into the weld and cause it to become very brittle and crack.

Cheap headers can be had for under 3000 kr, otherwise I'd try finding a professional to weld that. Which will probably be more than 3tkr.