Best Buy offers Prometheus on Blu-ray Disc for $7.99. Opt for free in-store pickup to avoid the $1.99 shipping fee. (Amazon offers it to its Prime members for the same price with free shipping; non-members can spend $25 or more to qualify for free shipping; otherwise, shipping costs $3.98.) That's $3 under our July mention and the lowest price we've seen. (It's a current price low by $10.) This version includes a digital copy plus both Blu-ray and DVD discs.
Update: The price at Amazon has dropped slightly to $7.48.