Popular streamers don’t accept every offer to demo a game.

True, but it also depends how many zeroes are in the amount. You have to find streamers interested in your genre, for sure.

do you know how much it costs to even get a small but recognizable streamer to stream your game?

Remember, Microsoft gave Ninja a $55m contract to stream on the now dead Mixer. And ofc Ninja mostly streams the most mainstream of mainstream games anyway. These top streamers are way more expensive than any ad program to just approach and inquire to.

anyways, to answer my rhetorical question: I hear the rule of thumb is either $0.10-0.20 per video view, or $1 per concurrent view as a starting point. you can use that to guestimate whoever you had in mind when you were thinking of paying a streamer.