True but we know for a fact that it doesn't consume 4-5 billion $ a year for the last 15 years like SLS/Orion because SpaceX couldn't afford that. If you actually do some basic math and look at SpaceX revenue and so on, you can make some pretty decent guesses. And SpaceX is analyzed in detail by lots of people.

I don't think "no idea" is fair. We don't have exact numbers, but there are various statements out there that give clues. Even the highest estimates I can put together put Starship far cheaper than SLS.

Even if a Starship needs to be scrapped after landing, the Super Heavy booster works, returns nominally to the launch site, and can be reused. This alone should make the whole thing cheaper than SLS.