Original price: $19.99
Sale price: $4.99
Practically a steal for MK9 if you ask me. It's not the best port, but it's worth buying for 5 bucks, and it's well optimized, also comes with settings that cater to low-end PCs.
For more information, as well as specs (minimum/recommended requirements to run the game) can be found here: http://store.steampowered.com/app/237110/