Musk makes an approximate $10/kg to (LEO) orbit estimate for full StarShip.
[Twitter]
Starship + Super Heavy propellant mass is 4800 tons (78% O2 & 22% CH4). I think we can get propellant cost down to ~$100/ton in volume, so ~$500k/flight. With high flight rate, probably below $1.5M fully burdened cost for 150 tons to orbit or ~$10/kg.