The cost of $4,000 doesn't take into account R&D costs, which must be recuperated in the drug's price.
Most drugs never make it past phase 3 trials, so fail in R&D before marketing.
Gilead didn't need a lot of marketing for its HepC cure to become a blockbuster and propel them to be the 6th biggest pharma.
DTC is also illegal in all countries except the US and NZ, so it's not even possible to spend that much. Sunshine Act in various countries, China putting execs in jail, etc. The world has moved on.
You can sell 1 million pills, at a cost of $5 each. That's a 5 million profit. Or, you could spend 80 million in marketing, and sell 2 million pills, at the cost of $43 each. That's a 6 million profit.
This is absolutely not beneficial to the first million customers.
Also, consider that the United States is the only country in the world that allows direct-to-customer medical marketing... Which is one of the reasons why the cost of healthcare is so damn high.
Drug companies don't increase the price to pay for marketing. Prices are set based on what the market can bear. A small drug company that decides not to spend a lot on marketing is going to charge the same as a big company that does spend on marketing.
How the math works is as follows:
$5/pill; 1 million pills sold with no marketing = $5M profit
$5/pill; 2 million pills sold with $3M in marketing spend = $7M in profit (66% ROI on marketing spend).