Paternity Test

I am just wondering how much it costs to get a paternity test...
My sons ex GF is pregnant and it might be his but it could be someone elses..
We would like to get a blood test before the baby is born..

I heard that there is a normal blood test that can be done now as their is fetal blood in the Mothers blood?

Out of curiosity I just googled paternity test and the first search result was www.easydna.com.au. They do prenatal dna testing on the mothers blood they charge $1690. It says they do the test from 10 weeks.