MapleStory Chaos: Profession Recipe Guide

It's not a vendor recipe. The only ring recipes you can buy are Swift Deadshot Ring I and [Stat] Ring IV. I mean, you can go and make Swift Deadshot Ring I and get the 5 extra EXP, but I don't believe it's worth 300k per ring.

Good to know if you're running against the deadline, but as you say, highly impractical, you'd need some 309 recipes from level 7 to level 10, at 300K a pop, that's 92.7M not including the fact that Diamonds currently cost more and are more scarce. Mathematically, if you take the number of number of Gold/Topaz from the number of Diamonds necessary to get from level 7 to level 10 you get 18. That's essentially 18 less rounds of Jewelcrafting (90 Fatigue) you'd need to do or approximately half-a-day of Jewelcrafting. That math seems wrong, not even I expected it to make that little difference, but until corrected, I suppose it does.