WA in January will be hot and flights $$. We went home to Qld from WA last Xmas and spent nearly $4000 on airfares and car hire for two adults and a toddler! It's beautiful here though, but maybe the wrong time of year.

I can vouch for Fiji - I've been in January and it was awesome. Doable on your budget too I believe. The afternoon storms were waay cool too

Is $5000 enough for a cruise? There would be heaps of choices over the school hols.