Deal is now dead.
This deal only works if you have Unidays account [myunidays.com].
Go through Unidays and you will find the S8+ Coral Blue Unlocked
on Samsung for $322.49 after $150 Trade in. The black one is $411.
You can find it under Back to School Deal.
The cheapest phone that you can buy to trade in is a 5S. You can get it on Walmart for $49.99
Be aware that Samsung has terrible customer service and Ingram Micro has history of rejecting trade in for random reason. You will be charged $125 if your trade in phone doesn't meet the requirement.
Best Case: $322.49+ $49.99 + Tax
Worst Case: $322.49 + $49.99 + Tax + $125
Good luck. I probably shouldn't post it before my orders are shipped. Samsung tends to ship LIFO.