Okay, the ASC hate machine can stop now.
Thread starter - what you are proposing is perfectly fine. If you leave the lower reciever in the states and bring everything back, you are doing the right thing.
If the cost works out to be cheaper for you, then that's great, also you can get some more unique AEGs that you aren't likely to find hoping it shows up on the classifieds. The cost is entirely yours and your decision. You don't have to listen to people telling you what they think about how it is a waste of time or cost more in the end. If you've worked it out for yourself and you think it's more cost-effective for you, then by all means, go for it. It's your money.
Aside from that, I just want to reiterate that your statement that "a lower receiver that is unsuited to be used in a real firearm is not prohibited" is false. What is prohibited from import is a replica. It has nothing to do with functionality as a firearm. If you are fabricating them in country, then that is a whole other bag of worms and if you have done your homework, then do what you want. Beware, the RCMP reads this forums.
"However, you cannot acquire, make
or import a replica firearm"