Ricey,
I too have years experience booking bands etc, you make some good points, however I'd expect Reece would be getting paid between 5-10K max + costs (flights, accom, transfers rider etc).
You need to consider that this is not a full blown concert, he'll sing 3 songs max + maybe the national anthem. He could catch the 8.20am flight from Syd to comfortably be at AA for an 11am sound check, perform, then be back in Syd for dinner.
I would say his management, in an effort to keep him relevant (which is SO important for any sustained success for these x-factor type talents) would be happy to have him take the booking for a reduced fee.
If I was running the show, and the Hilltops weren't busy with touring/recording I'd approach them to "Host" the whole event + perform at Halftime. Debris could DJ throughout the event and they would legitimately help to promote the event. It would be an awesome day, probably do it for 10k tops - no real extra expenses flights/accom.
Mastin would be a good booking if they genuinely used him effectively in a significant amount of promo. If they paid him 5K then spent another 10K promoting it correctly they would only need to sell an additional 250 family passes to cover these costs. He's kinda the right type of "family friendly" booking, so not terrible.
Alternatively they could get Mitch Creek's favourite hip hoppers to play - Watch the film clip he stars in: http://vimeo.com/49103434