The very cheapest method of doing a TT would be, as Rarly said, installing twin turbos on 930 engine and kepping CIS.
You could pick up two second-hand Garrett T3's for 300$ a pop, sell your wastegate for 300$ (T3's have internal wastegates), buy some tubing (maybe 600$) and get trigger-happy with TIG.
That way you could get your beloved TT-setup under 2000$ (including oil-piping etc.) but you'll need to fabricate lot's of stuff yourself and use OEM intercooler which isn't the best.
Of course, we are talking modifying 930 here, modifying 911S would be price-prohibitive....everything would need to be replaced: Pistons, intake, injection, brakes, transmission etc. etc.
Blown: ordinary steel can be used in turbo, no problems...what do you think OEM 930 exchangers are made of?
