I have a lot of experience in this area of teaching.
Expect good experienced teachers who know there stuff to charge £30-£40 per hour. But normally pupils take. 20-30 min lesson. You can get teachers who charge less and they may also be very good. Group lessons actually can be very good, especially as beginners. Having somebody to learn with can motivate and make it more fun.
If you have lessons through the local music service and take individual lessons you may actually be paying more tha the teachers normal rate. ( think hourly rate for the teacher + on costs of employment, + running costs for the music service) but you do get the ease of having the lesson in school time and / or a commitment to keep tuition going ( one teacher leaves they will supply another etc)
If you are doing this kind of lesson through a school or privately do keep close tabs on what the teacher is doing. It is far too easy to have teachers coasting and not pushing pupils. Speak to other parent s and try to find out about good teachers in your area.
And yes as others said, what the teacher does is only a small part of it, get your kid to practice, and be proactive in working with your child yourself (even if you know nothing about music just listen and motivate). It is a fantastic thing to be able to play music !