Upgrading the turbo internals is a good way of keeping costs down. I used the following company
www.turbotechnics.com to install better internals to increase performance internals. I was a bit skeptical about this as the standard set up was struggling at much over standard and I didn't think changing the internal components would make that much difference. However , it did, requiring less boost, creating far less lag, a much flatter power curve and lower intake temps.
We also swapped from the original flywheel sensor to a trigger wheel on the front pulley. An electronic boost control solenoid. It has forged pistons and rods. Changed to a coil pack from a distributor. Upgraded the knock and oil pressure sensors. Installed an inlet air temperature sensor. Upgraded the throttle position sensor. Lamda sensor in a bigger bore custom exhaust. Bigger injectors (260cc I think, I'll double check) which required a simple adaptor kit to fit. Ditched the air flow meter. Ditched the standard intercooler for a PWR charge cooler. This wasn't all fitted at once but incrementally over a few weeks and many dyno runs to overcome fueling, temperature and power curve issues.
Depending on what output your after you certainly don't need all the above, but the further you go the less the factory set-up can cope with it and so you are effectively developing an engine with a miniscule resource budget as compared to the original manufacturer
As is the often the case with my projects I start with much more enthusiasm than knowledge regarding how to do it and the costs involved, but then would I go ahead (and miss all the fun) if I knew all that in the first place? While making no great claims for my progress i think I'm now getting somewhere near on this one