Since everything, even the sand for cement must be brought from the mainland your build costs will be significantly higher than there. Usual average costs for a well appointed, western style villa are expected to be between 4 and 6 million IDR/per sq. mtr. Be ready to pay well above that for your island home. Best place to check might be worth a trip to the Gigi's where you'll find quite a few western builders/owners willing to chat.
sorry but these days are over "well appointed western style villa" for 4-6 million Rupiah / m2"
Of course it makes a difference if you do all by yourself or hire people. But honestly who of us will build with his own hands?
To find somebody GOOD who WANTS to build for you BECAUSE it's profitable for HIM is more important. Good contractor find a job everywhere and who wants to have a house from a bad or incapable builder? I don't...count 10 million / m2. I plan on 1000 € / m2
oh and that's Bali prices. I almost once bought a complex on Nusa Lembongan "Playground". didn't happen because of some shady nominee.
As Markt said everything is coming by boat from Bali.