SFRC sells them for $30 when they're in stock.
http://www.theammosource.com/index.php?main_page=product_info&cPath=14_103&products_id=593
SFRC (Norc), $35, Milarm (Norc) $50, Marstar (Unknown brand), $35, etc. It seems all the new Norinco magazines have welded floor plates shut and riveted. The original "flavor" of these magazines are now like "bacon bits" at your local grocery: they taste like bacon, but it's NOT BACON! $50 is way too high for a 5/20 magazine. The 5 rounders come up in the EE all the time for $20 or less or even 3 for $40!
I too am in S. Ontario and the local guy here(in Steeltown) had the M14 for a few $ more than I could have bought online. He also has mags for the same $50.
I bought the rifle from him anyway, he threw in a few extra's without me having asked him.
A few days ago I bought a couple of the 5/20's too. He's been a good source of info and advice. For that I'll gladly pay an extra few dollars to support my local dealer.