Armory by etotheipi is capible of running as an air-gapped offline wallet for bitcoin.
Raspberry Pi is a 35 USD / 1 BTC computer that is meant for children to experement on and learn computing. It also happens to be the perfect computer to dedicate to a bitcoin offline wallet. You can buy a pi for less than a bitcoin here. The instructions that follow will get you a binary of Armory that will run from a raspberry pi that has never touched the internet.