I'll just echo the while GC seals. 50k seals will net you about 600k gil selling crafting mats(depending on MB). Just roll on all the loot from dungeons and turn them in. Ex dungeon gear gives you 1100 seals per piece.

With casual play you can get back to 50k seals in just a couple of days. 2 to 3 mil a week isn't too shabby for just running dungeons.