You can certainly buy a ready-made drink mixing robot if you're flush with cash, but wouldn't you rather spend that money on the drinks themselves? Yu Jiang Tham thinks so -- he recently designed Bar Mixvah, a robotic bartender you can build yourself with $180 in parts. The key ingredient is an Arduino Nano microcontroller that takes your requests through a web-based interface. After that, it's mostly a matter of 3D printing the frame and wiring up the pumps that will make your beverage a reality.
Bar Mixvah definitely isn't a simple project; you'll need to be comfortable with both loading Arduino code and soldering connections. You'll also need a 3D printer, so the final cost will be much higher if you're starting completely from scratch. However, it may be worth the time and effort -- in the end, you'll have both perfectly made drinks and the tools to create other things you fancy.