Custom fabbing a manifold is going to cost more, or the same as, getting a turbo kit. Also, with the intercooler and other parts, you may have to make custom mounts to mount everything into the car, which also costs money. There are also no directions (since you got a Mitsu kit) and not many people can help (since most people buy kits). So if you don't know all that much, I would suggest getting a turbo kit, since it will probably be cheaper and people on this and other boards can give you more help with it.