The iPad mini 3 is and iPad 3 are two completely different tablets. The main difference is size. The iPad mini 3 features a 7.9-inch Retina display and the iPad 3 sports a 9.7-inch Retina display. The iPad mini 3 is powered by Apple's faster A7 chip with 64‑bit architecture and M7 motion coprocessor, and the iPad 3 is powered by Apple's older A5X processor.
The iPad 3 is discontinued, but the original iPad mini, which is still available for purchase, ships with Apple's A5 chip, giving it somewhat similar specs as Apple's third-generation 9-inch tablet. The original iPad mini is also the most affordable Apple tablet currently on the market at $249.