Well, if you plan to record your flights and monitor them dont forget another $100 or more for a DVR monitor.
Hobby king has a tiny fpv set up much like the spectrum thats around 7g of weight and less money... but its a monitor thats going to throw you over your budget.
If you choose a larger quad its a much easier task to get into a budget fpv set up...In any case, expect to pay near $150.00 to do fpv with your nano QX
If you go with a larger quad such as a Syma X5C-1 you can get both the fpv set up and the quad itself for less than $100.00....Do yourself a favor and avoid the syma X5W wifi fpv model or the X5SC models for other reasons....the wifi fpv is garbage on any model or brand.