when I have done the guttering on the outside for customers I have charged them starting from £50.00 upwards just for one side of a property if they have it on all four sides then I charge £200.00 also depends on the access requirements.
For inside the guttering it can depend on how bad the mess is inside them, but again it depends on what you want to charge and how much time you are willing to put in.
My best price I have ever picked up just for external cleaning of gutter, fascias, and soffits was £295.00.
Hope this helps a little.
Kind regards.