How about a mic from Behringer or Dayton and software from several sources. Eg: ARTA , Virtins,ETF,Audiotester etc. All are not exactly the same but they need a good sound card to give good results. Check them out.Most have a free demo download to see what they can do. "Might" work out cheaper than ZTX.
Behringer and Dayton mics are calibrated I think. Dayton ( EMM6) calibration can be downloaded from their web site when you enter the mic serial number. You will find lots of answers to your question on the web. It's been around for quite some time ! Google it.
I've recently seen the Behringer mic ( ECM-8000 ) in a shop on SP road in Bangalore.Try Bajaao.com also ! You do get good sound cards also. Software is downloadable.