For what I'm looking for - no, they're not too high.
Sure, you can make the calculation this way: If a girl works 8 hours per day, with half an hour between clients, at £100/hr, then she'll make £500 to £600 per day, before expenses. That's a lot of cash, sure. But if a girl does 5-6+ punts per day, then frankly she'll be shagged the fuck out, and what you'll get is a prossie with a thousand-yard stare and mechanical service. For most prossies, there's just no way to recalibrate your sense of enthusiasm for the work for more than a few clients a day -- for some, maybe a few clients per week.
Call me a fluffy, but I like to feel an actual connection with a girl. This requires her to have some real enthusiasm for her work, and that requires her to have not to been shagged raw by a conveyer-belt of other blokes. When I pay more for a girl's services, it's with the hope that I'm paying for some of her personal time off as well, so that she's not all shagged out when I see her.
Occasionally this backfires of course, and I pay £150/hr for a girl who's obviously servicing a conveyor-belt and provides mechanical service. Other times I go for a cheap punt and am surprised to make a real connection with a girl who's genuinely just doing this for some extra spending change. (In fact my best punt ever was £100 for an hour -- and we hit it off so well that she kept me there for an extra two hours, gratis. That was exhausting). So it's not a always a correlation between quality of service and money. But I've generally found that they're fairly well-correlated, and there's a good reason for that.
Now if all you're looking for is a couple of holes to blow your load in, then yeah, and you're not particularly fussed about connecting with the person on the other end of it, then yeah, £80/hr is too pricey for that kind of service. But for what I want, it isn't.