I'm trying to do this efficiently, but without much effort.
I did about a quarter of the way there today (maxed smithing 7 times, mining once, had 30 or 31 Diligence, now at nearly 50. Calculated it'd take 31.25 times maxing it when I started.) for ~30mil, consumed slightly more Super Moo than I'd expected (5 more, didn't account for crafting all the opals) - used 180 Super Moos.
My current process is
1.Buy 300 opal ore + 150 basic molds
2. Craft as many as will max the current mining level (or 150 in one shot) until they're all opals.
3. Make 1 less set of arrows than maxed the level last time.
4. If dilligence's bonus kicks in, I'm done. If not, make the last one.
5. Level up, go back to 3, until at level 10.
6. Start over.
Mixed in of course are dropping the arrows, and using up Super Moos.