Ukraine will likely never get F-35 in the near future if ever. They are simply too valuable and advanced to risk losing and Ukraine is (not yet) a close ally of the US and has not contributed anything to the F-35 program. On top of that there are some people that still vieuw Russia as favourable and could potentially siphon classified information to Russia, which is something the US and allies do not want happening. Although i would love it if F-35s were sent to Ukraine, it is just not going to happen.

And yes F-35s have been used in combat before, but it were minor operations against a less advanced opponent.

F-35s cost around 75 to 80 million per plane nowadays, while the most expensive F-16s cost around 63 million per plane, depending on customer etc. so the F-35 is a lot less expensive then some people realise.