Ok maybe there is no need to justify it but, if the question/ topic arises, I'd prefer to focus on the reasons my cost of living is more expensive (including basic needs such as visiting my family) rather than say "I'm better than you, get over it."
I always find proof-reading their writing now and then helps to subtly nudge them towards the latter conclusion, though, especially if (when) you find loads of mistakes. My co-teachers frequently ask me about pronunciation, grammar, etc.
I have to admit I'm not as hot as some of them at explaining the intricacies of grammar! Sometimes it's "just right"!