Private candidate GCSEWatch
Is it IGCSE or GCSE Combined Science?
It is probably a reasonable price.
That aside, £150 is not unusual for the fee to take a GCSE,
I got 33 in combined science and a 4 in maths however I need at least 7 in these subject to get A levels(further maths,computer science, IT). I revised everything during the lockdown period, so I'm feeling confident that I can get that grades or more than than. and I chose to do in November because I don't want to waste another year till summer.
Aim for 7s but most colleges in my experience colleges/ sixth forms only want 6s. However the odd college/ sixth form will want a 7 in maths to do a level maths which I think is a bit much but that’s just my opinion. Try to get 66 in your combined science which is defo achievable and a 7 in maths you should be fine.