I'm sure you probably already did the math and thought of this, but just in case you didn't, the cost for the highest level of gem (stone of ...) is rather obscene.
If the gems necessary for each level is 3*previous level, the cost for a stone of ... comes out to 3^10, or a bit over 59000, of a gem. If the cost is what I think it is (cost of each level = X column in the chart), a stone of ... costs 3^3*4^3*5^3*6, or 1,296,000 of a gem, which is a bit much. Like I said, I'm pretty sure you already did the math, but I'm posting this just in case you didn't.