Fun fact, 'cost' is a regular verb in Canadian English. Infering from the lemmy.ca instance, the comment op might be a Canadian, which means the usage of 'costed' is correct.
I am Canadian, and I was taught Cost as past tense in school and university. I've never seen it written Costed for past tense in any government publication either.
If only a very small handful of people make the same mistake, it doesn't evolve the language, it's just a mistake, plain and simple.
I know you're just trying to make yourself feel a wee bit morally superior by saying that, but it's the complete opposite of how language evolution works
People have varying degrees of ability to understand outside of what they know, what is "good enough" for you might be incomprehensible to someone else.
Would some variant of "snauk(t)" or "snaught" work for you? Your brain might be expecting ablaut in the style of "teach" / "taught" or "catch" / "caught" rather than that of "sing" / "sung".
How do you feel about "(p)reached"? "Snaked"?
A fun fact about "caught" is that it's a relative neologism. It uh, caught on after people decided they didn't like "catched" for whatever reason. (I guess it has something to do with tangibility / concreteness. Most other -atch words are used for objects.)