As I said before, Sedo is not in offic over the weekends, so the best times to ask them questions is Monday-Thursday, so they have time to asnwer before the weekend. I assume Keith will answer you on Monday.
I am still presonally a little confused on this point. Are you saying that you only point names with primarily UK traffic to Sedo? Or are you saying that you take each name you have and try to send some of the traffic one place and some to another place for the same name? For example, if you owned Sedo.com, you are trying to park the UK visitors at Sedo and the US visitors at Parked? Maybe this is your problem, if that is what you are attempting. Perhaps I am just misreading.
The fee for selling on Sedo is a flat rate 10%, which includes the escrow service. You will not be charged anything extra, unless you purchase additional things from Sedo, such as their domain brokering service or an appraisal before selling it.
The minimum selling price on Sedo is $60 USD. This is basically them saying that they don't want to handly any transactions on their system for less than 10% of $60 or $6. To answer your question, you would be charged $10 total on your $100 transaction.