And by "out" I mean, under 10mil. Awakening Max Cyborg was pretty expensive, but besides that I don't know where it all went. I know there are transaction costs associated with leveling up, etc. but I didn't expect to get so low.

From Fudjo's Guide to Asset Management--
Runes are going to be far and away your biggest expense for Gold. To fully level up 6 Talismans for a character, you'll end up spending about 2 million Gold.
That must be where it all went.