1. Make a Jett
2. Skip tutorial
3. Accept all the quests (8coins)
4. Make sure you accept level up quest
5. Get to level 13.
6. Open Phantom Envelope (3coins) [You can stop here if you need something with 11coins or less]
7. Get to level 15
8. Finish level up quest (1coin)
9. You now have 12coins to buy w/e you want
10. Continue for more or profit now
11. Repeat

Credits Go To: MeMagicalPie

*You could just use FMA to level up your jett if you need more coins then repeat, just saying.