Lowest cost programmer to burn bootloader?

I'm more or less cloning a MKR zero board for a project (slight tweaks) and will use a non-programmed SAMD21 chip, so I will the ability to get the Arduino bootloader installed.

I just read that the Atmel ICE ($expensive) can be used is there a less expensive option that someone has used?

Can anyone explain the process or provide a link?

Thanks