There are a couple of Arduino sketches that will burn bootloaders onto other arduinos very quickly.
I was first with "Optiloader":
https://github.com/WestfW/OptiLoader and it's probably simplest (but harder to upgrade, and not so well documented.) Also, it's designed for very fast bootloader programming: connect a cable from the arduino with the sketch to the target arduino, hit reset, and wait for the target power to cycle...
Adafruit followed with their standalone programmer:
https://github.com/adafruit/Standalone-Arduino-AVR-ISP-programmer which is more general purpose and less bootloader oriented.
And the most recent is Nick Gammon's "Chip Programmer" here:
http://www.gammon.com.au/breadboard (this one is probably the best-documented, especially WRT burning bootloaders.)
AVR programming is via SPI, with no inconvenient high voltages, and RPi theoretically supports SPI as well, so in theory you could write a quick programmer for RPI as well. Or apparently avrdude will run on RPi:
http://kevincuzner.com/2013/05/27/raspberry-pi-as-an-avr-programmer/(beware voltage levels, though!)