What I'm ending up doing is go higher one month and lower the next. Telstra pre-paid 4g.
Basically, get whatever 40-70 bucks one month, use up data and call credit until it lasts and pop a data pack on when needed (700gb). Actually, first month didn't need a data pack at all because sim=30 + top up 40 gave me enough. That 70 bucks roll over into month 2 so I can get even the 30 dollar recharge and get data out if the now 100 bucks I've got sitting there. Works out really cheap.
Besides, the data pack runs from when activated. Really nifty.