You can get it super easy in the U.S. for cheap

Here is lab grade caffeine

That if you wanted to make 150mg energy drinks it would cost less than 3 cents each.

If you want to just mainline caffeine I would recommend caffiene pills they are preportioned and are cheap here are the equivalent to 100g pre measured out for under $20

But my point still remains that the cost of caffeine is completely irrelevant to the cost of energy drinks

That’s because monster overcharges, caffiene powder is cheap and you could add it to soda for cheap

The heat of vaporization is also a huge negative of using water as you need to condense the water and then reboil it which wastes a bunch of energy