I also explain how to burn a bootloader to a 3D Printer that doesn't have one yet. But really, you might not even need one!
Use a USBtinyISP as a programmer or re-purpose an Arduino board you might already have to upload anything even to mainboards that do not come with a bootloader installed.
USBtinyISP drivers (Windows) https://learn.adafruit.com/usbtinyisp/download
Get a USBtinyISP
Aliexpress http://s.click.aliexpress.com/e/ctRyQ4Sy (get one with the cables)
Cheap Arduino boards
Arduino Nano http://s.click.aliexpress.com/e/2PwETWC
Arduino Uno http://s.click.aliexpress.com/e/b52ipsmM