Something of this nature would be sufficient for a very budget minded setup. A 420a flange should be cheap and having it welded on in place of the 4g63 flange won't be too costly. Spend an extra $50 to have reinforcement brackets welded to help distribute weight from the runners better and it should be a decently reliable manifold. I understand you are budget conscious with a build such as this, but if your OVERLY cheap, you will never have any sort of a reliable setup whatsoever. Expect to spend around $1200 to turbo a 420a with good knowledge of parts and what will actually work.

MITSUBISHI EVOLUTION 7-9 STAINLESS STEEL TURBO MANIFOLD | eBay