GoG has a spring sale, and SC4 Deluxe is 75% off ($1.49, if I recall correctly).
Checkit out here: https://www.gog.com/?utm_medium=email&utm_source=newsletter&utm_campaign=20170306_spring_sale&utm_term=EN
Pretty sure 75% off $20 is ~$5, but that's still a good deal (unless you mean ZAR?)
I'd get it if I hadn't already bought it from Amazon during a different sale. GOG is a great platform.
It says 75% off = 4.79 € for me, so that seems to be the "standard" discount price. Surely worth the money if you don't have a copy yet. :)
Ah sale time, the couple weeks of the year when SC4 sells for the price it should be selling for all year round... don't you love digital...
(Seriously, this game was £5 in the shops whilst it could be bought on CD, for many years, yet suddenly is 4x the price on digital stores? Check Amazon today, the disks are still cheaper, it's madness).
Anyhow, it's a good price for a short period, plus for my money the GoG version is outright the best. Completely DRM-Free and the only version to include the -CPUCount:1 switch by default, which let's face it you're going to want.
Sorry! Was typing on my mobile. The 1 issupposed to be a 4