There's no cantrip with an actual cost.
Odd, there are a couple cantrips listed here with material costs... Things like Dancing Lights, Mending, and Message. Or are low-level materials like that just considered as "covered" by a component pouch without having to specifically get them?
Of course, I suppose it's possible that this page is just willfully misleading, because after all, "We're not the PHB".
I wouldn't agree that you could use it to polish something to almost frictionless either, since that doesn't fit the definition of cleaning. You're magically removing the dirt from something, not actually scrubbing it down.
The difficulty comes when the object you're cleaning can itself be considered something that would be cleaned away... Such as "cleaning" a patch of dirt. Do you let someone dig a hole until there is no more dirt, or do you let them be more specific and define what dirt is dirtying the other dirt?
I'd heard the "polish a stone into a mirror" example given by someone who presumably knew a thing or two about the spell's uses and abuses, so I figured it was something people did. Still though, hiding in a kitchen and incessantly cooling a dish every time it comes off the stove seems like plenty enough reason to take Presti, even without a DM who lets you just *poof* goddamn keys into existence... I'm ashamed to say I missed that definition.
I mean, if your group is okay with those kinds of munchkin shenanigans go ahead, but if they aren't then all a character like that does is wreck the game for everyone. Not a judgment against you for wanting to play that way, just an observation of standard group dynamics.
Well, I mean, there's munchkinning and then there's munchkinning... Like, I of course want to make an effective character who can hold their own in a fight, but I also don't want to just make Minmax the Warrior to stomp upon all comers, because that gets boring.
Disguising wine as strawberry-flavored popsicles and terrorizing the local children sounds much more entertaining to me. Or abusing Minor Illusion's description stating that "you can create a sound of any volume", and hardballing a negotiation until the other party will do whatever it takes to
please make the floor stop screaming.