The Freezerburn...heavy lift cheap...here's how:
Saturn I style cluster tanking...'tis been done before.
The way Freezerburn does it, is by clustering four Lilmax modules into a big single core stage. Two end structures act to tie the modules together, and carry the extra-huge recovery system...which might include funky inflatable heatshields depending on how fast the core module gets going.
This (very unlike Saturn I), is strapped with ordinary Lilmax modules. Up to 12 such modules can be wrapped around such a core, often with strap-to-strap crossfeeding in the larger configurations.
The only all-new item is a huge (compared to existing) upper stage with a diameter of 9...perhaps even 10 metres. It is assumed that this upper stage is not recoverable, since its dry mass performance is paramount for most conceivable missions...however...like certain station proposals involving the S-IVB upper stage and Shuttle External tank, it would make an excellent pressure vessel to be reused in space, enjoying a long and fruitful service live without ever returning to the surface of its homeworld (although this doesn't rule out landing it on another world, like the Moon, for example.)
What the heck would you need such a huge booster for anyway? Why would you want to make it cheap?
The short answer is something that the Ascent Roadmap doesn't answer directly: passenger access to space. Space tourism is a high potential industry (can't say "booming" yet), and once these tourists start getting to orbit, they're going to want destinations for their cramped little shuttles, somewhere to go stretch their legs. They're going to want space hotels. What better to launch a luxurious space hotel than a cheap, reliable Freezerburn booster?
There are other potential markets too: Lunar, Martian, NEO, Libration zone construction. 5m diameter modules and flimsy inflatables eventually lose their appeal. Freezerburn will be needed eventually.