Depends on the coach and if you book a package deal.
I currently pay around £16 per 30 minlesson on a package deal. My old coach was £24 and I preferred him.
The only way to know if it is a good deal is to take half a years worth of lessons (one a month or so) and see how much your handicap drops! Other than that is how much you like the teaching style etc and that can also take a few lessons to know if its right.
In summary you cannot tell till you have shelled out at least £100