jamie cheapest option is to put some splits in .. 1.5 hp in your bedroom and office
and maybe a 2.5 in that living kitchen area should cover u

for ducted in the roof will be in the range of 6k plus
easy..

1.5hp can be had for $500 each ish
2.5hp around 1k i can get them installed for u too.

the people who are doing my air con can do it..

i chat to u when ur online next... about it. i can get the aircons too if need be from rick hart,