Yes you can! You do have to pay to resit but I am 90% it's not about £80. I think it depends on the exam board but I retook two WJEC AS exams this year and i think they cost about £21 each. I still have the resit letter for this year and although they could change next year I listed them below so you have an idea of how much it could cost.
AQA
£21.05 per unit
EDEXCEL £24.30 per unit
OCR £22.30 per unit
WJEC
£15.32 per unit