fuel costs are a small portion of launch costs.
Really? What is the expensive part then?
Engine development/manufacture, mostly. The shuttle used 610 tons of oxygen and 100 tons of hydrogen which cost approximately $200,000 based on market prices. The cost of the solid rocket booster fuel is unknown, but one estimate is about $2,000,000. The cost to launch that bird was $450,000,000, so the fuel was half a percent of the launch costs.