Depends on what your growing in, open beds or pots? are you going synthetic nutes or are you going organic or a mixture how often will you be watering, how hot does it get where you are and about a million other questions.
I make my own soil personally, but the Yates organic stuff for $7-9 a bag is good, the cheapest stuff is a good base if you buy some bags of perlite (not from bunnings they are crazy expensive) some dolomite and a big ole bag of dynamic lifter, then mix it all up sand let it sit for a few months.