Some points well made above. However, learning at a 'field with "tower" ie Air Traffic Control will inevitably be more expensive than at a field with Air to Ground radio, or Airfield Information Service. (You will get used to radio work with either of these.) Further, airfields with an ILS (Instrument Landing System) will also be more expensive as they have to charge more to maintain the infrastructure, and until you have a licence you won't be going anywhere near instrument approaches. (There are none in the area you specify anyway) In addition, Instrument traffic always takes preference over visual flight rules and student traffic so you are much more likely to be delayed before departure or landing, leading to a cost increase.
If you are based at or near Hatfield you should certainly investigate Panshangar at Welwyn. (I had my first lesson there in 1958!) It's friendly and with perfectly good student facilities. Elstree - about six miles from Hatfield - is another option with two schools, hard runway and facilities which are improving rapidly under new management. And Stapleford is also a strong contender, but further east and more difficult to get to.
Visit Elstree and talk to people in the cafe (not the Three Greens Restaurant) the lady proprietor is a fully qualified instructor, and Panshangar before making any decisions....
PM me if you want more Elstree details....