First there is a fork of Organic Maps, which is called CoMaps. If I understood it correctly, the development on Organic Maps nearly halted for some reason regarding the company that owns it. CoMaps now wants to pick it up again.

Also for navigation I use Magic Earth. It uses OSM data but is not FOSS itself, which is unfortunate. But it offers traffic data which is crucial for good arrival time estimation or avoiding traffic jams.

IANAL so please don’t take my word for it. But if I understood it correctly, this is indeed legal. You don’t have to offer your stuff for free. And as long as you let the user decide if they want to pay with money or with data, it’s legal. The important part is, that the user needs to give consent, which is the case here. Not talking about the morality of it though.