This one will take a while and will probably be your last achievement. Smaller coins are worth 50 and larger ones are worth 1000. Aside from money vases there isn't a quick way to do this besides grinding on enemies and picking up their loot. Money vases will show up on the map after 32 Mark of the Gods are collected and might speed the process up a bit. You can check your progress in your book by pressing once. One good area is the hidden Jungle: In the Treetops area, as it's packed with enemies. Can only be done in single player.