As barfo said, Warren Buffett could handle the cost. So could many other billionaires or corporations. Hey, exon just nuked Spain. But even so, it's illegal, not just expensive. Although big nukes are mega expensive, you could build a dirty bomb for a few mil. (Cheap smoke detector is ~$8. 100,000 smoke detectors contain enough of the isotope americium-241 to make a powerful dirty bomb.). But large sales are tracked by our government and you would be arrested for building such a bomb. How many Americans could afford a few million bucks?
And yes, when the 2nd amendment was written of course it meant everything they had at the time. But the biggest baddest thing at that time might be able to kill a dozen people at a time. We now have weapons that could kill millions. That's a it of a game changer. We also have many more people and much easier access to due to relative affordability of all our legal weapons.
In my fathers lab back in the day he used to work with palytoxin, one of the most toxic things known, made by some sea creatures, can't recall exactly. He needed it as a way to study a specific cellular pathway, but part of the way through his experiments the government banned it, even for most scientists. My father ended up smuggling it into America for his experiments. Because it was illegal and could be weaponized. That was over a decade ago, my father is retired and the substance has long since been destroyed.
Nukes, dirty bombs, mustard gas, and a whole bunch of other things are illegal. No matter how you want to say it's just economical reasons people don't have them, you are wrong. There are laws, laws and more laws.