I've done loads of these, and honestly 50 or 60p is a bit low IMO. If they are any way dirty at all, and if the client is any way fussy at all, charge at least £1 as detailing around those little brackets can be a right pain, and very time consuming. If you can just rub them with a microfibre and move on, then 60p a pane might be ok,....
Last time I did panes like that I charged 3 each,... but they were particularly dirty and very awkward access!