I've been doing this for years. Back in the day you could charge quite a hefty fee but nowadays it is different.
I tend not to charge for temporary hosting of smaller <200MB offline/web files during edit and for a short time after completion for transfer of files. I offer it as part of the service - many of my larger clients either have their own FTP or use DropBox/YouSendit so the free or low cost options are so abundant I would feel particularly bad charging for something that can be found for a very low cost.
But certainly I charge for any time taken up compressing/transcoding and for uploading. But this is done at the cost per hour of the suite and my time (at my lowest fee if I don't need to babysit the progress bar or full whack if I do).
If you are hosting it on your Mac network and
not externally then look at similar FTP services and be competitive; albeit with the added security that you offer by not going to the cloud and an external FTP which can be viewed by the service admins.
However if you are doing very large very high-bandwidth then you need a dedicated server. You can get hosted 250GB dedicated servers for about $135 per month - here is a service [
www.365ezone.com] [for illustrative purposes only I have never used these guys]
Like any service - work out how much it costs you - mark it up a bit; covering setup and running costs and charge accordingly.
Tell clients the options up-front, and tell them the cost and time involved in data-wrangling. As long as they know what, why, when, where and how much then they are usually more accepting of the charges involved - especially if they need the service.
If they say they can get it cheaper - let them arrange it - but make sure your contract puts the onus on them for any issues.
For instant answers to more than one hundred common FCP questions, check out the LAFCPUG FAQ Wiki here : [www.lafcpug.org]