The cheapest metal body I've seen is the Element AK74 one that goes for $25 on www.rsov.com
. The potential savings are there is it weren't for the stupid border guards enforcing the stupid laws.
Metal body from shady overseas retailer - $20
Shipping to Canada - $40
Potential criminal record for trafficing prohibited devices, 4-hour border waits and the possibility of having to reassemble your CBSA-stripped car with a screwdriver at your point of entry every time you come back to Canada - $Priceless