I think you'll get as many different replies as there are people on this forum, but never mind - being a pilot is about learning to look at all the facts and then make decisions as much as it is about learning to manipulate the flight controls.
There are two ways of looking at this...
1) You can only afford one lesson every two weeks, but you want to learn to fly now. OK, so do it that way. Your progress will most likely be slower than someone having more lessons, as you'll forget things in between lessons. OTOH, you'll have time to read all the books, pass all the exams, spend time talking to pilots, and learning a lot of useful stuff that others won't have time for. You can hang around the flying club, get to know people, maybe get taken on some flights. It may take you a couple of years, but they'll be good years, and you'll have something to look forward to every two weeks.
2) You can save up, and then do it. It will probably take you less time in actual flying hours. But you won't be able to do a lot of the above. Yes, you can study and pass the exams first, but a lot of the theory makes more sense if you're doing some flying. And will it be as much fun as having a regular but occasional lesson to look forward to? Only you know that.
So, you see, it's your choice.
As for after you get your PPL - you can spend more, or less. Hourly hire rates are cheaper, certain aircraft types are cheaper, more experience means you can leave longer gaps without your skills degrading so much. But you'll get bored, possibly, with short flights in the same area, and you may want to do more, and spend more.
Again, it's up to you. But being a pilot is about making your own decisions...as I said at the start. And sometimes learning to do that is the hardest part of learning to fly.
