I have NO IDEA how much the Club pays for the paper envelopes in which the magazines are mailed so I can't make a cost comparison.
I can, however, say that the cost of Tyvek envelopes would be around 29 cents (probably cheaper in the quantities we would require) per envelope.
http://www.associatedbag.com/product.asp?cn=ABC&c1=ENV&p1=ENV&c2=T350&pid=34%2D3%2D01
This was the first vendor I came across and I didn't investigate any further.
Yes, my magazine arrived today with one end of the envelope nearly torn off.