keep in mind the manifold is not only going to be subjected to a LOT of heat (moreso than a NA manifold due to the extra heat caused by the backpressure created from the turbo) but it also has to support the weight of the turbo and downpipe and resist any sort of play if the motor torques against the IC piping/exhaust which are usually stationary.
a turbo manifold needs to be able to put up with A LOT of stress and also effects the cars peformance based on the efficency of the runner-design and wastegate flange (if applicable)
I know it's hard to cough up a large chunk of change for a good manifold but if there were one thing i didnt skimp on it would be the manifold.
I just thought I'd toss my $.02 in and bring up some factors you might not have considered.
http://www.cheapturbo.com <-good source for brackets and flanges if you're going to fab something up yourself.