Had a friend just go through this exercise for his 50ft cat. He found as you go north the slip fees
get more expensive especially around Mackay. The theory is that with the mining boom the cost of living has gone up (3 bedroom houses rented at over $400/week) so everything else follows. He finally settled for Bundaberg Slipway in the town reach of Bundaberg itself. I know this further south of where you asked but I hope it helps.