A potential collaborator applies for a grant on his own: what should I do?
I am somewhat surprised about the answers so far. The behavior of the professor as described seems at least a little unethical at best, and downright exploitative at worst. If a more junior researcher comes to you with a good idea and some first steps towards a concrete research plan, and you answer with (basically) gee, good work, now please excuse me while I do this research with my own students, I have a hard time seeing how this would be in any way considered fair. Asking the OP to be happy because he "helped progress science" after all is ... ok, I have literally no good word for this expectation. As we all know, reputation is the currency of science, and it sounds like the OP was badly short-changed.

Whether the professor "needs" the OP or not is, to me, not really the important question here. The OP had the original idea, so it is unlikely to assume that he would be entirely useless in the remainder of the project. Hence, cutting him out of the research basically right from the start seems really awful. The least you can do is take him on and give him a chance to contribute to the research - if it then turns out that he or she actually lacks all the relevant knowledge to contribute from the project from then on (unlikely), you can still decide together to part ways later on.


  And, moreover, is this type of behavior acceptable? Do I have any leverage here? Do I need it?


I wouldn't consider it ethical at all. Whether you have any leverage is another question - likely no, as (as correctly noted above), just having the idea by itself does not warrant co-authorship (but you should have been given the chance to do more), but it is kind of too late for this now.


  I'd be happy being involved with the research itself, but I'm not sure he wants that. He'd probably be best off career-wise keeping it to him and his students (and, mind you, this is a researcher who puts a lot of effort on career advancement - he's an equally talented businessperson, albeit in academic research, as scholar).


As I said, it is a bit late to ask for co-authorship of a thing that's already been written without you. If you don't actually want to be involved in the rest of the project, I am not sure what you can realistically ask for. In this case, I am not sure if you can get much more than an acknowledgement that you brought the idea to the mind of the professor. 

(that being said, I wouldn't touch a collaboration with this guy anymore for the rest of my life)