Like many social services they are probably underpriced. How much would you charge for any old stranger to come to your house and fuck you?
I used, in my fluffier days, to entertain this view but the more I think about it, the more I believe it's ridiculous.
Many people do jobs that are physically unpleasant; mining, working with waste and so on. I'm not saying these jobs equate exactly with the job description of a prostitute but while such jobs do tend to be accompanied by a salary premium over jobs that are available to people with similar qualifications (which is to say no qualifications), their salaries are nowhere near those of a prostitute. It may be that working in McDonalds pays 5 quid an hour and requires no schooling. Someone who works in waste removal (insert similarly unpleasant job if you don't like that example) which also requires no schooling probably earns more. But maybe 7 pounds an hour and not the 120 a prostitute earns. Where does that random figure come from?
The point is, the decision to let strangers come to your house and fuck you doesn't determine the appropriate price. If you don't like it don't do it...but not liking it doesn't mean the world should pay a fortune so you can more easily come to terms with your own personal tastes. Supply and demand should make the calculation for you. Thus, while working girls can and do charge what they can get away with, in reality their prices go up and down according to demand. As a rule, parlours -- where larger numbers of girls can be easily accessed -- are good barometers of value. 50-60 quid for half an hour (with a room thrown in) and 100-120 for an hour is roughly the going rate and given that that is probably roughly 15 times what most working girls could likely earn in the open job market (before anyone says so yes, I know there are always exceptions that prove the rule), they are doing damn well at those prices. 7 quid an hour for shovelling shit; 5 quid an hour for flipping burgers, or 100 quid an hour for getting my gash bashed. Well, you work it out. The job may not be pleasant but the rewards are pretty good, given the alternative. And if you don't like them...
In my view, anyone who charges more than the above is having a laugh, albeit quite possibly a lucrative laugh, and anyone who pays more is either dumb or obsessed. The former won't be getting my business and the latter won't be getting my respect. I imagine neither will care.
In a purely calculated/objective sense, WGs should probably charge about 35-40 quid an hour based on comparable rates of, say, properly qualified masseuses who do somewhat similar work but deliver arguably more objectively measurable benefits as a result of actual training and recognised qualifications. If prostitution were legalised -- even better, if girls had to be qualified to do the job (in which case service standards would balloon upwards overnight to the benefit of us all), I suspect the price of an hour would drop towards, if not quite as far as, this level. In truth, 60 quid an hour is probably quite a sensible and appropriate price.
Personally, I don't begrudge paying 100-120 an hour or its proportional equivalent. I think it's just about fair and anyway, for me represents acceptable value but in my book, anyone who pays 200 an hour is simply barking. To do so damages the interests of us all.