Hi,
Cheers is correct, it is an iformal way to say thank you especially in Australia.
That's right, but a couple of words of caution.
This usage is now common in the UK, too, thanks to the all-pervasive Australian TV soaps.
However, I'm not sure I've ever heard it used to a large group of people, or as the closing word of a speech, however informal. In my observation, it tends to be a one-person-to-one-person expression. It is also socially a bit tricky. It has an aura of "mateiness" about it and so is inappropriate even in some otherwise quite relaxed situations. And women use it less frequently than men (in the "thank-you" sense that is) unless they want to come across as "one of the boys".
Sometimes it is also used in a sort of equality-asserting way that expresses a streak of inverse snobbery that Australians and British speakers share (but is much rarer in the US or Canada) For example, a couple of minutes ago I paid our window cleaner and he said, as he always does, "Cheers, mate!" as he pocketed the cash. He wasn't trying to be offensive and I wasn't offended, but there is an undertone there of signalling "Just because you live in a big house and pay me to do your dirty work, that doesn't mean you're any better than I am, so there!"
So it's one to be used with care, especially by speakers not wholly at home in the culture of those they're addressing.
Personally I would wind up a talk to such an audience with "Thanks a lot".