.. or half a million.. is the most suitable then..

I pledge my support for Mr Trowel: half a million! Still, I'm surprised that out of three responses, two are incorrect, so to clear things up... - half a billion/a half-billion (the second example is an adjective) is 500,000,000 - "thousand" doesn't receive an "s". You're not counting "thousand"; you're counting "five hundred thousand ______" Five hundred thousand dollars, five hundred thousand widgets, five hundred thousand shoes, etc...

five hundred thousand or half a million

Interesting, maybe just a half billion....!

five hundred thousands...