If you REALLY don't care about cost... here's what you can do.
1. Like wrxkid said, you can get a twinscroll turbo with titanium internals (such as the vf36). Since you don't care about top end, it will do the job well. If you REALLY don't care about top end there's the vf38, which also has titanium internals, but it's smaller than the vf36.
2. In addition to tiwnscroll and titanium you can shorten the exhaust and intercooler piping by doing something similar to this guy.
As you can see, since his turbo is right behind his front bumper, that allows all the header runners to be much shorter and also similar (if not equal) length. Your headers (with the twinscroll turbo) will be 4-2 as well. On top of that, the turbo will be breathing RIGHT into the intercooler, which in turn will be exiting RIGHT into the intake manifold.
3. Of course you'd have to do all the typical, boring stuff too. That means turboback exhaust, 3 port bcs, port and polish absolutely EVERYTHING, ceramic coat everything on the exhaust side, wrap the headers, external wastegate, antilag (if you want) built block (pick your displacement, but obviously more = faster spool), and dual avcs heads, with engine management, of course.
If you do all that, you'll easily be over the cost of buying another wrx, but your car will be BADASS!!! Can you tell I've thought through this before? Sigh... if only I had money like you.