I would say that syndicates that I've seen generally split about 60% chocks, 40% tacho. I can't recall any I've known charging airborne - although I'm sure some exist.
I'm in a syndicate at the moment that charges £100/hr tacho for an AA5a based at a medium sized airport and I fly ~65% power most of the time, my last few flights worked out about £85/hr logged. Tacho works particularly well because it tends to strongly encourage members to treat their aeroplane gently.
G