Hi Lorelei,
It’s difficult to give you a figure because it depends on the extra, and, like everything else, it is really subjective.
I’ll give you an example.
I charge an extra £40 for filming (which I rarely get), but other ladies are charging £100 plus.
If you state what extra you are thinking on charging for, then others can give you an idea, but the best way to gauge it, is to look at other advertisers in your area and see what they are charging.
The other thing I would mention, is that if you overprice extras then it is likely you won’t get many, but, again that depends on how many clients you want to see.
There are so many variables.
I like to be busy, which for me, is 5 clients a day, so my rates and extras are very average.