I concur with RarlyL8 and Tom on their suggestions. If budget is a consideration, start with known factors (base turbo engine), then convert from single to twin turbos using as many off-the-shelf parts you can. You're not necessarily doubling the boost, just using two, smaller turbos to eliminate lag and broaden the torque curve. Thus, your budget centers around two turbos, wastegate, associated lubrication and drainage needs, exhaust and intake system fabrication and an intercooler. You'll have to research the turbo size for your configuration, HP/torque @ ? rpm objectives, but there are plenty of books and sources to assist.
Once you have your TT working the way you want and you haven't yet grenaded the engine by experimenting at 1.5 bar, then you can assess how far the change in your wallet will go toward upgrading the inside of your engine. In other words, you might want to tackle this in steps.
As so many projects end up, you may tire of this idea at some point (or run out of money) and decide to cut your losses. This is not nearly so ruiness as building the ultimate long block (relatively easy but expensive), then having to finish with fabricating the rest of the system (not so easy, could be more expensive) that may not even work as designed.
A big difference will be how much you can't do versus farming it out to someone who can do. Because of this factor, I wouldn't even hazard a guess as to a realistic budget.
Sherwood
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