It might actually be cheaper even if the booster is expended.
Falcon9 is estimated to cost about $30M/launch. $20M to build the upper stage, and $10M to launch. Starship is estimated to cost about $100M to build both the booster and the second stage. Add $10M to launch.
$110M is insane. Anything under $1B seems unfathomable. $25M for a 2MN full flow staged combustion engine seems cheap. SpaceX plans on building them for $250K a piece. They're not there yet, but current estimates of $1M a piece are just as insane.
Falcon9 is estimated to cost about $30M/launch. $20M to build the upper stage, and $10M to launch. Starship is estimated to cost about $100M to build both the booster and the second stage. Add $10M to launch.
So 17t/$30M vs 150t/$110M.