How much is a QF-16 worth?
This has a pretty broad range of answers for this, but I assume what you are asking is what a flight ready QF-16 would sell for should it become instantly available on the civilian market.

Well the short answer is whatever someone is willing to pay for it.

The long answer is that aircraft values are based on a large range of variable, including, but not limited to, the value of the airframe, the current time and status of all life limited parts, currency of all required inspections, status of airworthiness directive compliance, avionics, outstanding repairs and overhauls, etc.

Now assuming this QF-16 is an acquired F-16A reclaimed from AMARC, with a reasonable amount of time left on the airframe, engine and all functioning avionics and systems as manufactured in the early 1980s by GD Fort Worth, the jet could easily command 15 million in FY2019 USD.  Now the QF-16 conversion costs vary depending on the contract signed but typically go for about 1.1 million per jet.  Add to that a dealer and/or brokerage fees of 15% sale price, the cost of flight training a reasonable budget might be 50 or so hours at $25,000 per flight hour or 1.25 million, this gives you an out the door price in the neighborhood of 19.6 million - that is if Congress will sell it to you.