I can tell you where NOT to try for reasonable prices - Airlie Beach Marina & Hamilton Island. I don't know about Mackay, I try & avoid the place. It has a big marina & hard stand. It was expensive in the marina in 2001.
Shute harbour has swing moorings & ?haul out - no idea of cost. Probably expensive like everything in the Whitsundays.
Bowen has pile moorings & some swing moorings & is cheap
but finding a spare one might be a problem. No hard stands
Laguna Quays is a cheaper marina on the mainland south of Airlie & Proserpine airport
& well run but isolated from anything else. Popular with some southern Oz owners for long term storage
Yepoon has a big marina and hard stand - moderately expensive.
Lots of overseas boats haul out
at Bundaberg Port Marina for extended periods - moderately expensive but well run organisation. Up the river in Bundaberg City reach, there is a cheap
marina with swing moorings where two boats I know have been left for long periods without hassle. Pay a little extra and they will check your boat daily & start engines etc.
My choice would be swing mooring
in Bundaberg city reach or Bowen piles.
Good luck & let me know what you decide and the prices for my information.