Award Questions

So I just finished booking a Itin from IAD-NRT-MEL and I noticed the site asked me If I wanted to outright purchase the itin for 11K vs. using 80,000 miles and it got me thinking what the most expensive tickets you could get using miles is. Bearing in mind I'm referring to a economy saver.

Also, I've always wondered how does the whole Star Alliance thing work when it comes to paying other airlines as most of my travel is on Singapore and ANA. Does United actually pay them 11k?

Cheers.