Susie, there really is no 'going rate' - it depends on where you are, what you're offering, how busy you want or have time to be and a thousand other things. I could stick my neck out and say ?100-?150 with the former at the low and the latter at the high end of average, but I personally know ladies who charge at every level between ?80 and ?350 per hour and provided you're happy with the amount of work you're getting that's all that matters.
Have a look around at the people near you who you would consider to be 'competition', or whose ads/offerings are similar to yours, then decide how you're going to work round them - you might want to undercut them slightly whilst you get started, or you might want to price your service higher if you don't want as many clients. Nobody can decide but you.
If you don't have clear boundaries (and if you won't do anal, you do have some) then that's the first thing you need to sort out. Read the
main site from start to finish and you should find lots of helpful stuff there
.