This could be the best opportunity to buy this stock in years.Beauty and cosmetics retailer Ulta Beauty (ULTA -0.02%)'s price action has been anything but pretty over the past six months. Slowing growth and slipping profit margins have caused the stock to falter; shares have fallen from nearly $600 to under $400 in just the past six months.Although the stock had reasons for slipping, the stock market often gets overzealous. There's a solid argument that Ulta Beauty's selling has gone too far, and shares are ...