Based on the weights provided by BWDD, if I didn't cat-cut, 7 yds of material would weigh this much....
70D 2nds (64" wide) 19.5oz
30D (62" wide) 8.84oz
I'll loose a little weight after cat-cuts, but it'll gain it back after reinforcements and tie outs are installed.
Here are the cost differences including all materials, hardware, and shipping.
70D seconds tarp - $44.51
30D 1sts tarp - $85.72