Price is no indicator of quality.
I've found much better instruction at a smaller, cheaper school than one which thought a lot of itself and charged accordingly. If you can afford it, have as many private lessons as you can in your first few months of learning to ride. You'll probably find that a half hour lesson will be quite long enough until your muscles develop. After a while, group lessons can be a lot of fun especially if there is a regular gang of people to swap stories with each week. You also learn by watching your compatriots get things right and from their mistakes.