Based on the density of the houses directly beside it you could fit up to (8*7=) 56 homes on the lot.

The homes on those lots are worth just about $1.5 million each. Fairly certain that's Aussie dollars, and that's $84 million total for 56 homes.

If the average cost to actually build a house in Australia is $320,000, that's (320,000*56=) $17,920,000 for constructing the 56 homes. That plus a $50 million land fee is $67,920,000. If all 56 homes sell for $1.5 million each that leaves $16,080,000. It won't all be profit but seems possible and doable if the $50 mil offer was also in Aussie bucks.