The answer you ask has a catch you seem to ignore: You can not boot a source file.
The core (installer, kernel, C compiler, other essential programs) will need to be downloaded as binaries. Additional package can be either pre-compiled or as source.
The best goal to minimize downloading would be to only download what you need. Start with a minimal installation set. Then decide which programs you want to add and how you want to manage them. Either via download as source (e.g. via a BSD ports tree or via Gentoo portage) or a pre-compiled binary. The last preferably in a package format such as rpm so you can not just install your system, but also keep it up to date without significant overhead.
As for an example: Those depend a lot on which examples you choose. The only fair comparison would be from a full system install (with average used programs) and to compare those. And then we need to start a discussion (with no clear answers) on what average installed programs are.