When farming Godly difficulty, do not prematurely buy the weapons until you farm all the necessary coins.

Weapon drops make up about half of your total weapon farm. If you buy out a fully awakened weapon (5 drops), you can still drop the same weapon while farming the other two weapons, effectively "wasting" 150 lilac coins.

Unless you want extra souls which can be a valid reason, you should hold on to your lilac coins until you can get all the weapons at once.

Anecdote: I've fully awakened and even awakened+1 from drops alone. If I didn't wait to buy the weapons later, I would have 10 or 11 of the same weapon.