People seem to miss the forest for the trees here. The goal is to get a base on the moon, and this is the first step. Starship will eventually be bringing lots and lots of cargo to the moon for this purpose. Bringing people there for a few days and then bringing them back is a very short term goal.
Falcon 9 launches every three days. It's not even fully reusable and it burns kerolox, requiring the engine be cleaned.
I doubt they'll have that cadence ready for Starship within NASA's ambitious timeframe, but if they can get orbital refuelling and full reuse working (which are big ifs) high cadence should only be a matter of time. And when you're just refueling it every flight, rather than building a bespoke new rocket (as with SLS), the cost for twelve launches would likely be significantly lower than one SLS launch.
The internal cost for a Falcon 9 is approximately 15 million, and that's including a thrown away second stage, drone ship usage, fairing recovery, and engine refurbishment.
