The space shuttle is a human-rated launch vehicle capable of taking 7 people into orbit at a total cost of $445M per launch, or about $65M per seat. When subcontracted to Russia, the charge was about $85M per person. Crew Dragon costs about $55M per person - which is one place my 10% number comes from.

Cargo flights are different, and you should also look at total program costs from the deal with NASA. The NASA contract [1] was for ~12 launchs, minimum 20T of cargo for $1.6B. That puts the total program cost at $80,000 per kg. The space shuttle program costs were about $60,000 per kg.

But don't take my word for it, here's a quote from a NASA scientist saying their payload cost per pound went up. [2]

  "My cost per pound went up with these rockets," Margasahayam told Tech Insider. "On the shuttle, it would be much less."

The article there cites per-kg costs at $10,000 on the space shuttle vs $27,000 on SpaceX. With the Dragon it came down to about $9,000 per kg, which is again about 10% below the price NASA was paying for the shuttle.

[1] https://www.nasa.gov/offices/c3po/home/CRS-Announcement-Dec-...

[2] https://www.businessinsider.com/spacex-rocket-cargo-price-by...