Re: Apples / Oranges
The correct price to orbit for the space shuttle is huge: get one from a museum, refurbish, $145M x 3 for new engines, $1B for a new mobile launch platform, ...
Falcon 9 prices are "competitive". That $6k/kg is either cheap and fast ride share with Starlinks - to an orbit you probably do not want or ride share to sun synchronous orbit (a popular choice for small sats) available about 3 times per year. The price is less than RocketLab or Virgin Orbit, but those two will take you to an orbit of your choice.
The Starship cost assumes the Starship is loaded to capacity. Do the same with a Falcon 9 and you get a price of $300/kg to LEO. Time waiting for a launch is a bit tricky: 5 Starships per year from Texas + 24/year from Florida - first launch real soon now (Elon Time). SpaceX has Falcon licenses totalling 100/year and may well reach that limit next year. The Falcon price is competitive with other medium lift rockets. The Starship figure is a theoretical cost to SpaceX. Prices quoted so far have been competitive with launching the same mass with a different provider.
For asteroid mining for use in space then you have to guess the mining cost and compare to cost on Earth + launch. For use on Earth then you have to guess the mass of platinum/irridium/... returned which could be very different from the mass of mining equipment launched. That launch cost per kilo is going to go up as maximum payload mass plummets for rides to the asteroid belt. Getting back your R&D costs will take time as the demand for the really precious metals is only a few tons per year.
So far I have only heard of one asteroid mining venture that takes the limited market size into account in their business plan.