Green Man Gaming offers Steam downloads of Goat Simulator for Windows, Mac, or Linux for $3.39. Coupon code "HAPPYB-IRTHDA-YGMG20" cuts that to $2.72. That's a buck under our Black Friday mention and the lowest price we've seen. (It's a current low by a buck.)
Want to enhance your Goat Simulator experience? Also available is the Goat Simulator GoatZ DLC for Windows, Mac, or Linux for $4 via the above coupon code. That's another price low by $1.