We do use Time4Learning. In fact, this year will be our 4th year! We have one in 1st grade, another in 5th, and our oldest will be starting their new High School courses.
http://www.time4learning.com/curriculum/high-school.html T4L is a really Great online program. It is super user friendly, fun for the kids, and easy on the wallet
~> ~> I have not ever heard of using coupon codes, but I do know they offer money back grantees and they also have a review offer ( they will give you a free month to try them if you give a review of your experience afterwards. )
Hope this helps