We used target formula for DS and it was great (we actually liked it better than the 'real' Enfamil b/c it had less bubbles).
you can call this number once every 30 days and they will send you coupons. I think it was for $2 off...
they don't offer 2 for twins - but you could have another family member call and pretend to have a child to get more for you :)
the # is 800.410.9629