Time, money, and lots of knowledge and skill. Actually, lots of time and money too.

It’s really not a practical thing for at least 99% of the population. Probably more like 4 or 5 nines.

For various definitions of "you." That's far beyond the reach of the average consumer.

So pay someone to do it for you. The free market has a solution.

It's odd how anti-hack Hacker News has become.

Sure. Other than being extremely expensive unless you've got the skills and facilities to do all the work yourself, and have the time and money to get all the engineering certifications required to make it road legal.

If you can do it all yourself, it's only moderately expensive.

In the us at least homebuilt cars slide through a lot of loopholes. And since you are coverting a car you automatically get many things that made the car road legal.