Resitting A Levels? (Looking for resit exam centres)

Hi, as the title states, I'm looking for a resit exam centre for A Levels a s a private candidate. I would like some recommendations for a good exam centre (efficiency / environment) with reasonable prices. I've seen a big range of fees for different centres in London and some seem really unreliable (£1k for a subject I've seen). Please does anyone have experience with / know about any good centres? Even better if there are states schools where I can just do the exams for free without having to study there. Thank you!