There are only two ways to get a computer running OS X, but without a permanently attached display. One is Apple’s most-expensive computer, the $2,999-and-up Mac Pro , the other is its least-expensive, the $499 Mac Mini. Other than those two bookends, Macs are all either MacBook laptops with clamshell designs, or all-in-one iMacs, with large screens on pivoting arms.
To get access to the features of OS X for same price as a standard iPad, you’ll need to bring your own display, keyboard and mouse or trackpad. If you already have some or all of those, great; if not, the total cost can add up quickly, especially if you stick to Apple-branded accessories.