F-16 also costed a fortune when it just came out of the blue prints and had only a few flying models. Guess what? It became the world's best selling firghter. Give the JSF project some time and let it mature. When serial production becomes online with many of the world's leading factories producing parts (outsourcing) and spending menhours, costs will naturally drop.
With its 9 aggressive partners and many planned orders and the project being on schedule, F-35 is in a MUCH better standing than the -almost-bankrupt Typhoon (Tranch 3). No wonder the UK wants to get out of it.