So I finally got around to making a small conversion table, if you will, converting some of the common in-game doubloon amounts into Euros, just to get a better feel for the cost.   The C column is based on the conversion rate of the 14,500 doubloon chest and the E column on the one for the 30,500 doubloon chest.   Upshot - if you like to buy economy flags, buy them in the game, not in the store.