US tanks were considerably cheaper compared to German tanks!! To understand this, we would need to understand the manufacturing process.
The US entered World War II as an industrial giant with many developed automotive factories and skillful workers. The US also had the most money and resources, that's why it could mass-produced huge number of tanks using fully established assembly lines - the same way they had been producing cars for years.
Let's take a look at some US tank factories:
Massive assembly lines, huge cranes overhead to move tanks along ....
... this room is simply huge, tanks lining up as far back as the eyes can see.
Isn't this how everybody produced tanks? Err ... No. The Germans didn't produce tank this way. Let's look at a German tank factory:
No great assembly line. And notice the ladder on the side of the Tiger tank? The ladder's there because the tank would stay in the exact same spot for a really long time, workers would have to climb up and down the tank again and again ...
See those the little white numbers? German workers had to scribble all over the tank to remind themselves of the manufacturing process: what had been done already, what still needed to be done, how big this hole was, what the distance between the holes .... You would never see things like theses in a automotive style mass-manufacturing factory.
Again, much work had to be done by hand:
While the Shermans were being mass-produced using automotive assembly lines, the Tiger tanks were *literally* hand-made. No wonder they were so darn expensive and there were so few of them!