This example sentence from (maybe) level 10, has 金 rather than お金. First example sentence for 最後.
お前に金をやるのは、これが最後だ。
This is the last time I give you money.
I was under the impression that when written, it should have the honorific to indicate it’s money and not gold. Is this not actually the case? Is it not like お茶 where it’d be bizarre/wrong to leave off the honorific? Or is this sentence supposed to be set in the past when some form of gold was used as money?
お金 is the polite (or basically neutral) way to say money, yes. This person isn’t being polite though, they sound pretty ticked off. So no need to make it sound nicer than they intend it to. I don’t think there’s much danger of it being interpreted as きん.
Basically, don’t use かね without the お unless you want to sound gruff or angry.
As an aside about 茶 and お茶, it’s true that if you are actually talking about a drink, you’re always going to use お茶, but 茶 can be used if you’re just talking neutrally about tea as a concept, as can be seen throughout the Wikipedia article on tea. For instance 茶の栽培は (The cultivation of tea…)