I don’t know if it’s an oversight by Square Enix but in the new squadron dungeons (lv 60 ones, Fractal Continuum, Pharos Sirius (Hard)),
they cost 3500 GC seals each per run, but u can get actually more seals back if u open all chest in the dungeons. And on top of that u get poetics from each boss.
Also good exp for a run (Lv 65 RDM, ca. 550.000 exp every 10 – 15 min) Pharos Sirius (Hard) is actually a bit faster. Maybe u can focus on this dungeon first. 🙂