Agree re: official Arduinos.

If you still want to use Arduino, I'd highly recommend going for Arduino clones from China. You should be aware that the USB chip is different so you may have driver issues, but I haven't had any issues on Linux. You can get an Uno clone for ~$3.

It's also worth considering moving to the Atmega by itself You can get the chip used in the Uno for $2, set it up on a breadboard, program it with an Arduino as the ISP, still use arduino libs if you want, and eventually move to a custom PCB.