UV Digital Now has Black Panther HD Full Code $5.49
PLEASE NOTE: It is Canadian Code but site provides instructions on how to redeem to US Itunes and UV.
This is the cheapest price I could find, I thought it would be a hassle to redeem a Canadian code, but it was simple.
Note: Code also gives 150 Disney Reward Points.
There are coupons available for orders of $50 or more. Look for Big Spender Offer on page.