Metal AR receivers are quite scarce in Canada due to import laws. You've already been a victim of multiple reciever seizures, so you know first hand how difficult it is to import such items.
It's the basic law of supply and demand that governs the price on these items. The high demand and very low supply, combined with the difficulty and high cost of getting these items into the country in the first place put a high price premium on them.
As was already mentioned, if you really want a receiver, the only surefire way to get one is to get age-verified and wait for one to pop up for sale in the classifieds. But you will be paying in the $200+ range for them regardless what their overseas prices may be. That's just the reality of airsoft in Canada.
So what it boils down to is you have 2 options - you either suck it up and pay the money for what you want, or you stick with your plastic receivers.