I forgot about that, you still have shipping, stamp duty and GST, so probably closer to $8k, plus labour
is the whole motor gone or is it just the head and gasket, if it's just the head buy a second hand one with a gasket and put it back together, if it's the whole thing then it depends on how much you want to spend and how far down the rabbit hole you want to go.
if your happy with how much power the car had before buy a motor of ebay, there on there for between $3000 and $4500, and drop it in.
if your chasing more power, pick a number and build it to that, no point spending $20,000 on a motor to take 1500hp and only run 600hp, on the same note don't spend $5000 on a motor to take 600hp and try a push 1500hp through it