Hi Guys,
I have about 80+ 5k class ISOs that will expire in 5 days. I currently have 10k gold, 3k BCs, 83k loyalty, and 1.1k units. By my computation, I roughly need about 500k gold in order to use these 80+ 5K class ISOs that I have. So my question is, what's the best way for me to earn 500k gold in 5 days?

The obvious answer would be arena - but seems like i would need 500 matches every day for 5 days just to get to 500k gold. The best bang for buck seems to be the 2* arena (wherein there's no cost to do a match, plus i earn 190 gold per match, BCs, and milestone gold and BCs).
Another thing I can do is to sell by basic ISOs - which is like 642 gold for every 1.3k basic ISO (which means, i need to sell about 8 1.3k basic ISOs to have enough gold to use 1 5k class ISO)?
Another thing i have abundance of are arena boosts, (i have about 1k+ arena unopened boosts crystals) but selling them is just like 100 gold per boost.
I can also buy gold for units, but that's just like 5k gold for 20 units.
Are there other ways or is there a better way for me to farm 500k gold in the next 5 days?

Note:
* I used to grind a lot, but now, due to time constraint, im now more of a casual gamer.
* I even rarely open any hero crystal nowadays because Im gold broke

so these ISOs are actually remnants of back when I was still pretty active in this game

Thanks