Sorry to have to throw this in, but there is no law that every DLC has to cost the same.
Theoretical I would buy everything that expands the game, but emotional I think the DLC-Business works better, when the
potential cutomer has a good feeling about the benefit he gets.
I personally would be willing to pay 5 € for the Quest-DLC, and in each case 2 € for the maps and the loot.
It is very nice from people to see the DLCs as chance to support the game, perhaps there are even chances to bring forward this idea, with rewards or special ingame-items for people investing more time and money into the game.
I like the system of Amplitude (Endless Space), they call it Games2gether, the active community can influence future content by voting.