Requiring battles to be approved by a judge has obvious practical problems, because they often happen in remote locations at unpredictable times, but Congress can pass all kinds of dumb requirements if they want to. That doesn't mean it's unconstitutional.
You're proposing an alternative where the executive gets to decide how money is spent. As if mass surveillance, which is a waste of money, has to be funded in order to fund ordinary investigations.
The executive is the weakest branch. It has almost no powers of its own, and shouldn't. It's checks and balances. For something to happen, the executive has to want to do it and Congress has to fund it. Not one or the other; both.
