All tandem jumps made in Australia must deploy the main parachute by 5,000ft.
15,000ft is the highest legal altitude anybody can jump from, without supplying oxygen.
The higher you go, the more freefall time you get:
6,000ft jump = 10 seconds
10,000ft jump = 35 seconds
14,000ft jump = 65 seconds
15,000ft jump = 75 seconds
All skydiving companies in Australia by Law are supposed to quote the total price including "APF Levy" or "APF Membership" and "Fuel Levy".
Cheap prices usually means one of 2 things - ie. tandem factory that gets you in and out as fast as possible and/or costs are getting cut somewhere...