How often does SMAC go on sale, and does anyone know when it last was?

The excellent website GOG Database started tracking this information in June:
https://gogdb.yepoleb.me/product/1207658936
Since then, Alpha Centauri has gone on sale only once, albeit with a very generous discount (75%).

It was also on sale last February or March, when I bought the game myself.

[url=https://isthereanydeal.com/search/?q=sid+meier%27s+alpha+centauri#/page:game/price?plain=sidmeiersalphacentauriplanetarypack]https://isthereanydeal.com/search/?q=sid+meier%27s+alpha+centauri#/page:game/price?plain=sidmeiersalphacentauriplanetarypack[/url]

So it refuses to turn into a proper link but you can either search for Sid Meier's Alpha Centauri™ Planetary Pack on IsThreeAnyDeal.com or copy and paste the URL above.

Thank you both for your replies. I've just finally upgraded my PC to Windows 10 (from XP), and it looks like i've got to replace most of my old disc-based games.

Just be warned, for gaming it is not a good idea to have WIn10. Be warned that some games WILL give you a headache or simply will not work on 10. And kind of get used too that after updates of Windows some games will (again) refuse to work. ;)

There are workarounds for a lot of games; see the specific subforums, search the internet or ask.

But yes, some games will never work. You can either keep your old, if still working, computer for those or install Linux + Wine next to Windows and have a good chance they work in there, not 100% though.