Rubies is the correct spelling, but in the screen that pops up if you attempt to make a purchase and don't have enough of them, it says not enough "rubbies"
First off, amazing game series. Great story, great style, great art. My only problem is that sometimes while going through the dialogue it acts as though I clicked the next button twice and I miss part of what was said. Even with this, the game is a solid 5/5. Well done!
@sadheart There is. Click the gear on the top right and go to controls
And HouseCentipede, look for stashes or keep doing missions so the mines you do have can produce
 "Idle Quest"){kind=icon}
 "The Journey Home"){kind=icon}
 "Ringside Hero"){kind=icon}
 "Soccer Physics"){kind=icon}
 "Trimps Preview"){kind=icon}
 "A Matter of Caos: Episode 4"){kind=icon}
 "5 Differences"){kind=icon}
 "Decision:Medieval"){kind=icon}
 "destruction"){kind=icon}
You can get it for free, I wouldn't feel right charging money for two really short songs. I'll PM you now with the link.