Sean W. suggested the idea of print on demand and digest-sized books, and suddenly my roots in the zine / indie comics scene of the 1990s came back in a flurry... what if the core rules are only four pages, and you print it on two sides of an 8 and a half by 11 sheet and fold it in half. You make your own mini-pamplet of the core rules. That's a dollar.
Then, there are several supplements that are immediately available. There's a monster one (same format) and maybe an adventures one (same format), and a magic one (same format). The monster ones could then be totally themed; common tomb inhabitants, mountains, ruins, deeper dungeons, the lands of flame... and each would only have maybe 12 monsters (a low level set of 6 encounters, and a higher-level set of 6 encounters for easier dice rolling). These are all pay what you want. Bam.
Every release for the game would be in that format. You'd be carrying around little 4-page focused pamphlets and referencing the one you need at the moment. An adventure would be in the same format.
Thinking more about this...