Prices really just depend on how many clients you want to see per week. I might be able to get 1 client per month at ?500 per hour working in the City of London (if I advertised right) - but it would be a big effort and I'd be spending a lot on ads. But if that's what I wanted, I would go for it.
Having only one day per week (or rather, about 3 days per month) now of available time for escorting means I need to encourage more inquiries while being much less flexible about times, so my rates are set accordingly.
To be honest, if ?160-ish is an 'average' rate for the City of London (an area in which bankers-about-whom-I'll-not-say-anything-negative-as-they-are-great-paying-clients are raking in zillion pound bonuses every year on top of bonkers salaries even in this recession), I'm not quite sure what I personally would charge on the other side of the country or in a smaller city in, say, Scotland. If I tried to charge the same rate, I would probably personally expect to receive much fewer inquiries (which might be fine as living costs would be HUGELY reduced, too). But then, I don't offer any specialised services and/or a porn star experience or anything; if I did, maybe that would justify my rate to a wider base of clients.
As already mentioned, it's best to thoroughly search across multiple listings sites and directories (NOT just Adultwork as the many fake profiles will skew your results) and review sites to see what rates are being charged and what rates are being paid.
For example, in London, many Pnet reviews (I don't read them anymore but did initially find them useful as a bit of an intro into what serious punters prefer) would say that they 'expected more' if they paid ?200+ per hour. E.g. they'd expect a luxury apartment, fancy toiletries, a really nice bathroom, big soft towels etc, not to mention a perfect GFE (possibly including A-levels at no extra fee) with generous extra time allowed for their showers. If I were able to offer all that (and able to be much more flexible with my availability), I'd feel more confident putting my rates up - but even then I might still keep them the same as they are now, cos isn't it better to get more serious inquiries than you can handle than to be sitting by a quiet phone?
Many reviews, I found, of girls charging below ?90-100 per hour in London were more likely to include complaints about bad showers, council flats, etc etc. *Not always*, I should quickly add! But it helped me get a rough idea of where I fit on the scale, as it were, offering what I do.