Amazon offers Prime members
Mirror's Edge Catalyst for Xbox One or Windows for $19.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $4.98.) That's $5 under last month's mention and the lowest total price we've seen. (It's the best deal now by $9.)
Exclusively for Prime members, it's also available for PlayStation 4 at the same price.