-Study Bones / Ooze / Tail are the three 80gil items which take 36 to equal a 3x multiplier. So, 2880 gil gets you 3x. If you're a Gil pincher, save money and wait until you can upgrade an item to max level in one shot. Save the investment to a one time shot at multiplier. Also, you won't need to level up any weapons until you're at a point you should be able to afford the expense.
-If you prefer to play and level up, do that--don't worry about the gil it costs you; just have fun and be happy.
-While Fluids and Oils may give more EXP, they're a waste becuasethe inorganic items are so much better. You are better offf getting to 3x as soon as possible, then switching to inorganic.