How much does a twin turbo kit cost (parts, labor, tune, etc) to put on a vw jetta mkv?

Not a good idea. Turbos always a trade off for more power at the cost of shorter engine life; but adding one is much more dangerous. And engine not built for it, will probably not last for more than a few weeks. The compression will be too high. A twin turbo in particular would really blow the engine up. Twin turbo makes more sense on a V engine, because it make the piping simpler. But on a Jetta, it would make it much more complex, hard to work on, cramped, etc. Minimum cost would be about $1500 for any turbo, and a twin would start around $3000. But to actually do a good job, would cost more like $10,000, because it requires engine modifications by turbo experts. It would probably be cheaper to put a salvage Touareg V8 in the car instead, and sell the old engine to keeps costs down. If you could find a Touareg that had been rolled, over for parts, then you could also switch the whole drive train, and have 4WD. That would have much better traction for acceleration and cornering. Although finding room might be hard.

the 2.5 would handle 12-15psi easy, you don't need twins. less than 5k for a complete install.