Firstly, welcome
To be brutally honest, if you're having to ask the question of cheapest PPL then you can't afford it. I know that is a terribly sweeping statement when I don't know your full situation but you need to be prepared for the truth of the matter and I don't want you to full into the headline cost trap.
A little time on the net searching for schools and clubs regardless of location will show you the vast difference in cost and little information regarding extras.
A few simple things to be aware of. You have got to be some natural born pilot to get your PPL in the minimum 45hrs if you are only flying once a week.
Lessons are often quoted per hour, however, once past the early stages the lessons tend to be over that and once you get to Nav exercises the lesson start to get expensive. Not such a big deal if you have a flying fund, but may be difficult if saving up before each lesson.
Don't ignore the silent wallet killer that can be landing fees which more often than not are not included in the advertised cost to get your PPL.
Also, location is important. No point in saving 15 quid per hour if you have an extra hours drive to get there.
And I feel the following is good advice generally but more so if you do use cost as your prime consideration, do not pay up front. Really, don't do it.
Like I say, I'm not trying to put you off, but as someone who is 30hrs into PPL I'm just mentioning stuff that I feel is useful information to someone starting out currently.
Again, welcome.