Currently, a single use SpaceX Falcon 9 can be purchased for about $62 million. The estimates for the cost of the SpaceX Super Heavy Starship (SHS) are about $250 to 400 million.
The current design of the SpaceX SHS has 38 Raptor engines. There are 31 Raptor engines in the Super Heavy booster and seven in the Starship upper stage. There are 9 Merlin engines in the SpaceX Falcon 9.
Lowering the cost five to eight times will require simplification of the entire rocket and mass production and lower costs for the Raptor engines.
Elon Musk also indicates that the cost per kilogram to low earth orbit will be at least ten times cheaper with the SpaceX SHS versus the Falcon 9.
Elon can also be looking down the road as his plans call for building about a thousand SpaceX SHS. This would require making rocket engine factories that have one hundred times the capacity of the current rocket engine factory. Currently SpaceX can make about 400 Merlin engines every year. Eventually, SpaceX would need to make 30,000 Raptor engines every year.