I paid for the licence and both tests and my parents paid for the lessons. My Dad didn't really have the cash to spare, but he said if I didn't learn at 17 then I probably never would get round to it. Plus after uni, I probably won't have the spare cash myself either.
My advice to you would be - go with a really good driving school, a really well-known one, whether it's a nationwide one or a popular one in your area.
There's one in my town, which everybody at 6th Form seemed to use and recommend and each of their driving instructors followed the same formula: 12 lessons, focusing on a different skill in each lesson. And then as many lessons as you need after that.
I also had a 2-hour lesson fortnightly rather than an hour a week. I found this to be beneficial to me as I couldn't get a lot done in hour really, having a good old practice and a long drive fortnightly helped me more.
I had no practice outside of my driving lessons and it took me from April 1st to November 13th to pass.