Calculating the average is about as useful as calculating what the average Londoner earns!
What I can say is that I did notice a few trends over the year:
Those with their heads screwed on know that it won't last forever, know that earning ££££££££ now is no good if you fritter most of it away and don't have a back up plan to earn at least £ later in life.
Many are not wise / mature enough to understand it, and make poor choices. Probably due to a combination of naivety, stupidity, lack of education, lack of financial literacy, etc. If you are in your early 20s and you make a few thousand pounds in a month it's easy to feel rich; it takes a lot of maturity to realise that your income is likely to fluctuate wildly from month to month, and that you need a plan for when you won't be doing this job any more.
A few of the WGs I have met over the year left while they still had decent options to do something else. I can think of 3, and they all said that they could do this job for a few years more, but the longer they remain in the job the harder it gets to do something else. One said she already had a degree and, when she left, finished a professional qualification. One said she had been accepted in medical school. Another said she would go back to her country and use the money saved here to buy a small flat + start a business. Obviously it could have all been porkies, but I did see the books of the professional qualification open and highlighted on a table!
The really high-end WGs, those charging £500+ an hour, really offer a different service to what is reviewed on this site. Many of those do overnights, long dates, weekends if not weeks away. If you look at their sites and profiles, they post pictures of being flown first class (not business, first) to exotic destinations, luxury dinners in Michelin star restaurants, weekends driving along the countryside on cars that wouldn't be out of place in a Top Gear episode, etc. I can understand that, if a punter has millions, spending thousands like this is nothing; what I do not understand is the risk of EAS (if you regularly book a WG for long weekends away you are no longer looking for an escort but for something else) and the privacy risks: those who do that probably bay by bank transfer, take WGs to their properties, so reveal their names and lots of details. This is a huge risk. But horses for courses.