Meanwhile the payload on the top is now "in orbit" but operating in a vastly different environment than the larger component, with different engineering constraints, quite likely using different types of fuel.
If you could couple the initial launch vehicle being "cheap and easy" with another system for moving around to different orbits or getting into even higher orbits (https://en.wikipedia.org/wiki/Skyhook_%28structure%29 or a "space tug" type orbital vehicle) now you have access to high-orbit/cislunar space, and you can start assembling your larger inter-planetary vehicles or space stations there. (Perhaps using a mass driver to move heavy but necessary things like water and other raw materials to the site at this point, but that greatly depends on what the cost-per-pound of launch can get down to, and what resources you can scrape up out of the solar system)
If you could get a mass driver system to work very reliably (more reliably than chemical rockets), I could see it being useful to deliver the critical assemblies of RTGs into orbit. Plutonium is pretty resistant to high acceleration. One of the main objections to putting a lot of RTGs in space (or even better, actual nuclear reactors) is what happens during a launch failure. A system that doesn't involve any fuel, and thus won't blow up and scatter the contents around, or require tons of containment, might be useful.
Nuclear reactors have a pretty nice energy-density profile, particularly if what you want is long-duration energy for interplanetary missions.
Still hard to get around the capex problem though.
Pilots try to keep plane flight take-offs below 1g. You could possibly increase the g load but not everyone is conditioned like a fighter pilot. Even supposing you could get up to speed faster, you'd have a lot more drag in the lower atmosphere. You can't really get up to any significant speed until you exit the troposphere.
And that means building at least 20km, straight up.
https://en.wikipedia.org/wiki/Laser_propulsion#Laser_Thermal...
Then send cargo up that's hardened for 30g in a vehicle launched from a 20 mile long mass driver that's tilted 45 degrees. We should be able to build such a structure by starting several miles underground, then building up the side of a mountain. 30g over 20 miles yields a final speed of about 9735 miles per hour. With a boost like that, the vehicle wouldn't need a 1st stage and could probably get to orbit without staging.
Make the bottom of the launcher a tube connected to some really deep part of the ocean and use massive floats to help support the weight of the structure then you have less structure to support in open air. You load the pods from sea level, then drop them down the rail-mortar and let computers and robotics handle the rest
Edit: oops, misread your comment.. sorry for the non-sequitur.