Pick your weights as part of the cashback special. Spend $150 get $75 back in points.
Add the $20 off $150 coupon if you have it in your account.
Total will be around $170 with tax for the three pairs in the title example. Plus $76 something in points that you can use to purchase the rest of the set later if you choose.
It is well below .40 cents/lb if you count the points.