Guys.. legit question here. When the government says "10M to build this small bridge" everyone knows a lot of that money goes to someones pocket instead od funding the bridge, like, a lot. Now, yes I don't know anything about how much does it cost to build a fab, but, isn't 1B a LOT of money? You know , one thousand times 1M, and Im pretty sure 1M can build like almost anything? So.. 65B? Rally? 6B gift? I mean
A few things you missed. Scale and personnel.
A small building for 1 million dollars, sure. Maybe a warehouse or a 10 office complex or a few tenant strip mall. A building housing automated fabrication machines and all its support structure, billions is an understatement. You have to think concrete, steel/aluminum, welding, HVAC, filtration (air and water) for clean rooms, warehousing (in/out), shipping, wiring/power, utilities (that power, water, etc don't come from nowhere), land purchase, environmental impact studies....
Now construction people have to be paid and building materials purchased. Architects and industrial engineers for the facility inside and out have to be paid, talking many millions and thousands of man hours to design such a facility. Inspections and permits aren't free.
Attracting workers, training, travel, etc. This will take a lot of money to do while there is absolutely no revenue stream. If you take the average US salary for workers in Arizona times the expected employees (12,000) then you get just shy of 1 billion dollars in salary alone, average, not what some of these high paid experts will be getting. Now that is once it is operational. Right now it is construction companies and consulting firms who are intending to make a profit, so they charge a lot more than you would think.
TSMC does about 360 billion in revenue, not profit. If a lot of money wasn't thrown at the problem, there wouldn't be enough of an incentive for them to take the risk.
Now, what does the government get out of this. Secure line of chips fabs within their borders. And eventually tax revenue from all the workers, tax revenue from the people who support them (restaurants, shopping, etc). And eventually tax directly from the business once their tax abatement ends. Government will lose some import tariffs though.
I work in the public sector with lowest bidders, and even the smallest jobs cost hundreds of thousands of dollars. Any significant project can easily be measured in the tens of millions of dollars.