I'm not sure how a school that selects the top 1% of students could even work, that would become a postcode lottery for the students who got in. Realistically could you travel to any of the closest 100 schools to you? Even if they were half or a quarter of the size of the average school and therefore there were lots of little super selective schools thats still going to be a massive stretch. 10 is probably the smallest number you could have and still have the grammars available for students living in most areas.
Extremely gifted kids have a special need. If a child needs to attend a specific school due to special need, then transport is the responsibility of the state.
I should add that I have a disabled child who is gifted, but not enough to make it into a school like that. He would do just fine in a good comp from the brains perspective - his disabilities mean he couldn't cope with the sheer size and bustle of one, though. When I say it should be for kids whose needs require a special sort of school, I'm talking extreme end of that spectrum.
I know a kid who had to sit in Reception learning phonics when he was already reading Roald Dahl and Harry Potter in his own time. And understanding them. At four. There is no skilful teaching or brilliant level of differentiation that can address that in a class with 30 kids, one teacher, and 1 TA. That child has a special need. Pure and simple. He deserves to go to a school that will challenge and stretch him - and he now does, because his parents are from a background that means he's now going privately, with a large bursary. But a child with those gifts whose parents didn't meet at Cambridge might well not have that option. Which means they will end up incredibly bored and disruptive, and never reach their fullest potential. They exist, and as far as I can see the best use of grammars is to identify and support them. Not to give already advantaged kids even more of a leg-up in life.
At present, grammars do in practice tend to provide kids from affluent backgrounds with a superior state education - a sort of middle way between state and private, in fact. All the argument about the provision of a ladder out for bright working class kids ignores the rather profuse quantities of data showing that they instead act as a ceiling, because poor kids almost never go to them. That's not a sensible use of resources, and on the whole it condemns those kids who didn't get in to schools that have low aspirations and low outcomes, from the age of just 11. That can't be sane.