Virgin Mobile has a deal at the moment Galaxy S7 for $55 per month + bonus Gear Fit2 + $100 credit. Includes unlimited standard national calls & text, $100 international calls and unlimited music streaming.
Galaxy S7 Edge for $65 per month with same inclusions/offers.
Resale on gumtree ~$550 for phone and $150 for the gear fit + $100 credit gives a 24 month cost of $520 or $22 a month. Not bad.