Ok, so it is not single platter and not quite $50.. close though, I would have expected it to be slightly cheaper in USA compared with Canada.
http://www.newegg.com/Product/Product.as...6-073-_-Product

these are $60
http://www.newegg.com/Product/Product.aspx?Item=N82E16822148395

I am sure there are other drives on sale for close to $50 now and then though.

If you want sub$50 then it looks like there are 320GB and 250GB drives and such as well.