No need to spend real money on adena farmers, if you can figure out how to macro farm you can earn enough adena to equip D, C, and maybe even B grades without even getting pass level 40 just utilizing the NPCs in Giran and Aden.
A party of 3 Dark Wizards starting from scratch can get from 20~40 and net you 2~3M within a few days if you manage to keep the party alive, unstuck, and hunting as much as possible. The Shadow servitor has a passive Vampiric Rage and helps them survive more. The summon's p.atk increases a great deal after every skill level up and they'll do all the damage, you just need to pickup and heal.
Go to Abandoned Camp and hunt Ol Mahums
Lv20~24 Guards, Stragglers, the weak ones.
Lv25~29 Generals, Officers.
Lv30~35 Commanders.
Go to Ant Nest next
Lv36~40 Captains, Overseers
The tricky part is to setup the party macro.