[PC] DRM-free - Steamworld Dig 2 - $11.59 AUD - GOG

While not the all time lowest price, this price is close to it and a great price for a great game.

From the website:

Adventure waits below the surface…

SteamWorld Dig 2 takes you on a platform mining adventure forged in Metroidvania flames. When an old trading town is struck by mysterious earthquakes, it’s up to a lone steambot and her unlikely companion to uncover what trembling terrors lie beneath.

Dig your way underground and explore vivid worlds riddled with treasure, secrets and traps.

Combat dangerous enemies at every turn of the underworld’s twisted paths, including shadowy creatures and the haunted remains of an ancient electrical threat.

Upgrade your gear to forge deeper into the earth and take on bigger challenges.

Swing across large chasms with your Hookshot and fly through caves with the Jet Engine!

And finally, learn the truth about your long lost friend…

Enjoy!