I'm going through this process with IRunGuns on the next export, so I'll let you know how it turns out. While you are charged the price of the complete gun, there is no (at this point) additional cost for the labour to break it down. You're essentially buying the full gun like normal, but only receiving the non-registered parts.
I didn't have much luck finding the spare parts I wanted in Canada, and at the end of the day, it worked out cheaper for me to get the parts through IRunGun's service --- bonus is that they're guaranteed to be OEM.