Are Variable-Geometry Turbos a good tuning option?

So I've had a question about Twincharging a F20C VTEC installed in a Caterham SV answered in a manner that advised against putting both a Supercharger and Turbocharger on a 4-cylinder engine from an S2000 into a Caterham that weighs little more than a quarter-ton. However, I would still like to eliminate turbo lag. I read that VGT's are good at this because they change in size as they spool up. I want to know, however, if this is a practical application on a petrol-engined car, and if it is affordable. I'm trying to write a fiction story that involves such a setup, but I need to be based in realism, to an extent.