1 Ether turns into 3 Mana stones, 4 if you buy that one book (Nephlune bookstore, IIRC) that improves mana stone creation efficiency.Mana stone gives you +2MP (if I remember correctly). I have ~50 MP so i need 25 more stones. Even if i would focus only on gaining it I think there is still not enough materials in the game at this point (as i said earlier I slaughter the most of the monsters already and also harvest all free pieces).
So that's 8 mana per Ether, hand over 20 Ethers, boom.
That's the way I made it to over 200 in my current save.
If you're struggling, which certainly can happen on saves where you just do whatever comes with the latest update, I recommend starting a NG+, and with the bonuses you take, try to get to the same point using Remove Collar fewer times, which is how you end up with lower corruption.
My personal favourite skill to unlock is Thunderbolt, as it saves you two days and +1K money spent learning it. That and/or the water veil thing (blanking on name, lol) are maybe the best NG+ skills to learn.