Unfortunately the in-game economy is going through a slump at the moment, due to players not spending gil and instead hoarding it to save for purchasing the land for their Free Company house (or Guildhall).

As a result, because no one is buying anything, crafters have to undercut/sell their items at a significant loss just to have a better chance of selling the item. Sadly there's no easy fix to this - until the land prices for housing reach their final level next month, the economy is going to remain pretty depressed unfortunately.

FATEs only give a very small gil reward sadly - you'll actually get better gil rewards through Guildleves and quests (quests especially often have very good gil rewards which get bigger the higher in level you are). So they are well worth doing as well.