The out-of-pocket costs to improve the internals of a NA engine for turbo use are lower than those required to achieve a similar power level, in large part, due to the fact that very high RPM is not required, nor is big CFM, $2,500 rockers, fabricated intake manifold, stepped headers, etc. An excellent 1,200 hp single turbo can be had for $2,000 from Precision.
Far more fabrication is required, but not necessarily highly technical - no structural engineering or flow charts needed.
However: money must be budgeted for post-construction adjustments. The difference between something that will go fast and not blow up, and something FAST is lots of dyno and track time (unless you're following a known path closely). The best combination of these factors will vary with ATM, boost psi, gearing, static CR, stall speed, spark, IC size and efficiency, and A:F. In some engines really rich mixture is the only safety net (short spark time didn't do it), and which engines is difficult to predict by design features (the ancient Studebaker V8 does very well). The 2JZ-GTE doesn't look at all special on paper (bore/stroke, port flow, rod ratio, valve sizes), but it delivers big power with tune up settings (psi, spark, A:F) that would be far less powerful, or dangerous in many other engines.
I chose the JZ in part because of my low experience with boost (Corvair and Buick GN only), and many known recipes already proven effective: I'm just following the footsteps.