Ok thanks. I am thinking of going with DDC for about $1600
Two or three women have written back with their experiences of prenatal DNA blood tests after they had them. Unfortunately, I don't think you will get answers directly from them -- like several of the other anxiety-driven communities on MedHelp, people who post here generally stick around only long enough to get their problem solved, and don't come back to answer others' questions.
Of the three women who wrote, two used one of the companies named in the following article, and one was in Australia and used a different lab. They all got accurate results.
http://www.nytimes.com/2012/06/20/health/paternity-blood-tests-that-work-early-in-a-pregnancy.html?pagewanted=all&_r=1&
Neither of the two companies in the link are the cheapest place that provides this service. However, there are reported issues with some of the cheaper companies (some that advertise heavily on the Internet are notorious for incorrect results). I'd keep that in mind when price-shopping labs, it really does seem like you get what you pay for in terms of reliable results.
Good luck!