It depends really.
Nottingham prices are now £80//£150 for half/hour generally speaking for a decent quality English girl. (Roms \ Thais \ Brazillians etc are cheaper, but I think they are more of a risk - do your due diligence)
For vanilla, I generally only book £80\half hours. Thats enough time for me to get a good grope, BJ and 69, a fuck and to pop once.
For extras \ something more kinky I would book an hour.
My general hard limit is about £200 an hour - and for that I expect one or more of the following.
Dominatrix \ kinky lady that fucks as well. (I used to see Dommes for just bdsm, but I've stopped doing that now)
Sub girl (for me, the definition of a subgirl is one that will accept a gag and bondage, hence the higher prices)
Filming \ pictures with my camera - I've taken some INCREDIBLE footage over the years.
Anal
I can afford more, but I'm afraid no vagina is worth half a weeks wages to access for an hour and I am very strict on monthly budgeting - I generally allow myself £160ish a month to punt, which is 2 x half hours or 1 long session. I look at some of the hourly rates (especially for London girls) and I laugh my head off - while people pay it, they will charge it.