Do you really want someone that offers dirt cheap lessons?
Wouldn't you rather have a high quality driving instructor that has a bit of a waiting list and is a bit more expensive but you'll learn to pass in fewer lessons and be a better driver?
When my friends have had lessons with dirt cheap instructors, they've all had to switch half way through.
I'm sure there are exceptions to the rule, but I'd always follow the viewpoint of WHY they have to offer lessons so cheap?!
But if immediate cost is the only thing your fussed about, look at low grade instructors in your area and ring them up to see if they offer a discount for block lessons.
I paid £18 an hour with my independent instructor and he was amazing. I passed in 20 hours and really enjoyed learning with him.
I think any less than £17/£18 an hour would make me a little suss. I'd have to question why they are charging that little, especially when you look at the costs involved [petrol, insurance, car upkeep etc].
I pay £18 an hour if I block book 10 hours, otherwise it is £19 an hour for students or £20 an hour for everyone else at my driving school. This is a regional one with a couple of branches in my area. I would suggest looking at your local companies.
I have seen a few places at about £18-20 but not much lower than that. I agree too cheap can be a bit suspicious. My instructor is good but she likes to drag everything out a bit, practicing everything so many times before moving onto the next manouvre, so she is getting more money out of me that way although she reckons this is to make sure I will pass first time, so if I do then fine, I will be satisfied with her method! Amazed at the person who passed after 20 hours at £18 each. Bargain.