multivitamins.net.au
Its a $3 billion dollar plus industry
Yeah big industry... .net.au so obviously not as good as the .com.au...
But considering that MultiVitamins.com.au is owned by OMG, there is a good chance that it wont be developed for years to come as they have other priorities, you have a great name which could secure a top ranking.
Plus no other keyword rich domain is ranked well, you have an even better chance of getting it ranked high.
As for what it's worth...? Undeveloped I'd say $800.