Im adding always parking lots with the Tag “fee” = yes / no
and found another good tag on the following page: http://wiki.openstreetmap.org/wiki/Mapping/Features/Parking
The access tag for parking lots.
In the simplest you can tag it with access=private.
I sometimes use other values such as access=customers(for shop parking), access=university(for staff/visitors of the local university) etc.
Later renderers, satnavs, and other applications may make use of some access=values but generally they will not want to direct users to access=private.
So you should be able to define all parking lots with those two tags the correct way.
I would not add the amount of money you have to pay for the parking. But If you would like to add it. Put it into the “note” field, so other people can later use it somehow.
