We hired ours privately (sadly we don’t have one any more though, hence house now unclean), although we looked at some agencies as well. Average for Yorks seems to be about £8 an hour and most wanted 2 – 3 hours to clean our small 3 bed semi.
Things to consider – do they bring their own cleaning equipment or use yours; if agency, is it the same cleaner each week (often they are not); what will they clean in the kitchen – a lot will not do the oven, hob etc.
Having a cleaner is lovely. sigh.