When it was first introduced in 1934 the tax stamp cost the same $200 as today but adjusted for inflation that's $5,000 in today's dollars. That was also deep Great Depression times while $200 is dinner at a nice steakhouse today. That fee was meant to ban them in practice without actually "banning" them in violation of the 2nd Amendment.
You're overlooking a historical fact, Congress specifically picked $200 because that was the original retail price of a Tommy Gun, which was the
cheapest and most common machine gun in America at the time. It's list price was $200 ($3,700) from 1921 to 1925, then they lowered the price to $175 ($3,300) in 1926, before raising it to $225 ($4,400) in 1928 which was still the price at the time NFA passed in 1934, at which point due to the Great Depression starting in 1929, the value of $225 would be $5,600 today.
Machine Guns were already unaffordable for the general public in the US at the time, and as a comparison, the only other machine guns you could find for sale in the United States were Colt Montiors which were $300, and surplus BARs and Lewis Guns that generally went for $250. To put it in perspective, the average cost of the cheapest new car in 1934 was $600.
As such, Machine Guns were only held for lawful purposes by the Government, Industrial, Mining and Commercial entities, it was exceptionally rare to find any law abiding private citizen personally owning a machine gun in 1933.
It's not like today where you can 3D print a Glock Switch with $1 of filament or make a lightling link with a 20 cent metal coat hanger.