As said, many charge wheels off to wheels on plus 10 and that is not too unfair as it includes taxi time but they seem to be charging taxi time twice!
In fact the AIRCRAFT hours are only wheels off to wheels on so a bit unfair to charge for taxi time anyway! Personally I would be looking at another way to go flying - but then I am in a group aircraft anyway so we can charge what WE decide and any surplus goes into the group funds.