20bil figure came from WSJ article from january. It's not something new.
WSJ News Exclusive | Biden Administration to Ask Congress to Approve F-16 Sale to Turkey
The $20 billion sale is contingent on Ankara’s approval of NATO expansion, administration officials said, and comes alongside a sale of F-35s to Greece.www.wsj.com
That number It also includes 900 AA missiles and 800 AGMs.
So it is not just the price of Fighters.
With those equipments EF will cost more.
F-16.net - The ultimate F-16, F-35 and F-22 reference
Lockheed Martin Corp., doing business as Lockheed Martin Aeronautics, Fort Worth, Texas, has been awarded a $799,955,939 firm-fixed-price incentive contract for F-16 aircraft production.
www.f-16.net
Slovakia's 14 f-16 contract with LM costs 900million but with extras 2.7 million .