Hey all!
I just through together a very simple gem calculator. You start by selecting the quality of the gems you are starting with, the quality of the gem(s) you are trying to make and the quantity desired. The output is the required mats you will need (starting gems, crafting gold and tombs).
Let me know if you find it useful and/or things that you would like to see added to help you out as a quick reference when crafting gems. Thanks!
diablo-3-gem-calculator.com