By Christiana Molina, Allure Magazine If you're any kind of beauty aficionado, chances are you have a Holy Grail product: It's that one item you can't live without, but much to your chagrin, it's hard to come by. Many of us have gone to extreme lengths—and paid extreme prices—in our ongoing quest. I once spent an admittedly absurd amount (over $100) to score M.A.C....