Here is some general information about fees of professional voiceovers
Voiceover fees are normaly no hourly rates, they go by the economic value, that the client wants to gain with the recording. This is why for example a TV-Commercial for a well known automobile-brand, which is aired in whole europe, costs a lot more than a Radio-Commercial, which is only aired on a local Radiostation.
So the first question will always be, for what the recording is used. I it used for a TV Commercial, a Radiocommercial, in a Imagemovie or for a Audiobook? Depending on the use there are totally different rules.