Well according to this person* by the end of WW2 a proximity fuze cost $18 or $314 today.

I figure I could probably put together a resilient fuze using off-the-shelf parts that's at least as good as a WW2 era one for Of course factoring in today's markup on military parts and the failings of military procurement, that fuze will actually cost the tax payer $3000-$30000 + R&D.

* https://history.stackexchange.com/questions/75940/what-has-h...