Hey troopers!

I'm relatively new to the game... I only discovered the forum a few weeks ago.
I was wondering what is the best way to increase ironite stock. After Bounty Hunter Eddie and Little Tim's event I've burned all I had.
I anticipate I will be unable to get top rewards in upcoming events without spending lots of $$$.

By only spending the daily 300 SoT (aprox), what's the best way to build-up ironite?
What I normally do is Skull quests and daily challenges, but is there anywhere that gives a nice ironite return?? daily dungeon perhaps? anything else I'm missing?
Thanks!