Abyss and Coral Sahagin behind the ornamented door in SSG drop nearly 10k each with gilfinder. They're level 75 mobs with more hp and Soul Voice and Benediction respectively. Easily soloable as rdm, bst, thf or nin. They repop roughly every 20 minutes so you can make some quite decent gil/hour killing them. That's where I usually farm. Competition down there's been going up lately though.
Btw, I've tried going after the equivalent mobs in other beastman strongholds (Ruby/Adaman Quadav, Yagudo High Priest/Templar, Orcish Warlord/Hexspinner) and they do not drop anywhere close to the same amount of gil as the sahagin.