Well first you need to determine what a Zuz is worth.  [Here is an article specifically talking about the 200Zuz of a Ketubah and it's various understandings, from $750-$1,000,000.][1]  Current custom in Israel is to not evaluate the actual worth of Talmudic coins but to equate it to purchasing power, technically known as relative worth.  [You can see this in action with US Dollars here][2].  According to the Rabbinate the current relative worth of 200zuz is equivalent to $50000USD [which is explained here][3].  Coinicidentally this past October I was maseder kiddushin in the US.  I asked Rav Ovadia Yosef before I wrote the Ketubah, if the $50k stipulation should also be included in an American Ketubah, where it wasn't mandated by state law and there were differing opinions concerning the value of a Zuz and he told me that it should still be written explicitly that 200zuz is equal to $50000USD.  

So 50000/200=250.  250*2=500.  So 2zuz is $500(or possibly considerably less if you follow another valid opinion).


  [1]: http://www.jlaw.com/Articles/KETUBAH.pdf
  [2]: http://www.measuringworth.com/uscompare/
  [3]: http://www.lawguide.co.il/articles/1119/%D7%90%D7%99%D7%A9%D7%94-%D7%94%D7%9E%D7%A4%D7%A1%D7%99%D7%93%D7%94-%D7%9B%D7%AA%D7%95%D7%91%D7%AA%D7%94-%D7%90%D7%99%D7%9E%D7%AA%D7%99-_9295/