SLS is something we are stuck with. "As we advance slowly it is getting less expensive to do things". I agree to some extent. The biggest issue is that there is no need to advance slowly. Now that SpaceX and Blue Origin can propulsively land boosters, building the SLS is a bit like building a Zeplin with modern technology when a modern airliner should be built.
SpaceX Falcon 9 isn't enough rocket for anything beyond orbit. Falcon Heavy can, but barely. It actually competes with the Delta IV Heavy, which is now obsolete. It's more rocket than SpaceX can currently market.
SLS is the rocket that Space Buffs love to hate, true, but it is near to ready for launch. next year it will be an available rocket for moon missions.
Unfortunately, the heavy SpaceX rocket, the Starship isn't ready. The orbiter is not ready for test launches yet and most likely won't be for another few months. They haven't even started work on the Heavy, the first stage booster Starship needs to reach orbit or anywhere else off the ground.
Blue Orgin has nothing that is ready for orbital flight either. New Shepard is strictly sub-oribital. New Glenn has nothing beyond the motors and one half of a faring actually produced. It's months at least away from being able to launch, and it's also strictly orbital, like the Falcon 9. The New Armstrong isn't even that far along. Those are the best rockets on Earth for these proposed missions.
So we are stuck with using non reusable rockets for missions beyond low Earth Orbit for a few more years.
Elon Musk is currently promising sometime in late 2021 for the Starship assembly. Like many others, I note that he sometimes makes rather hopeful promises, so I won't count on anything before 2022. But if 2022 pans out, then yeah, I would gladly pay a tenth of the price for twice the rocket.
Sorry, but the "Zeppelin" rockets are all we've got. The "Airliner" rockets simply don't exist yet.