Done, $112 CyberNav with Orux. Cheap enough to be near disposable, and awesome with the kinks worked out. Review
The biggest problem is the screen as (so far) cheap generally does not equal sunlight-readable. My answer to this was custom high-contrast maps (near black and white) and a sunscreen. Of the two, the high-contrast is the most important.
Oh, and yes, OSM data and my tracks through JOSM (map editor), through Maperative to generate my very own tile-set (high-contrast, thick lines), through MOBAC to generate Oruxmaps. Yes, Orux configuration is crazy, but awesome when you get it right. Yes, the multiple learning curves of the above are crazy, but I am very, very happy with the results.
I've been meaning to do a write-up on the above... but then I've been meaning to do a lot of things these days,