We have applied and hidden costs are a worry. More of a worry is putting a child through exam stress, knowing that the children at the Indies own junior schools have had in house prep for the exams. With no past papers to work on, even with a tutor it's not exactly a level playing field
If you are referring to The Grange I have done a little research for you I know quite a few parents and children who attend there at prep and senior level.
The entrance exam is CEM computer adaptive test i.e the questions asked are dependent on the previous correct answers .
There is no special prep provided by the The Grange Junior School for this test.
Prep kids are not guaranteed a place at Senior School it is an open competition with pupils from other Primary/Prep schools.
However 70% of the senior cohort originate from their own prep/junior section.
If your child is within the top 25% of the national cohort they stand a very good chance of passing and being offered a place.
Almost all exams at 16 at iGCSE's but only A levels are offered at 18 no IB or pre-u A levels
Oxbridge entry is between 10-15% and out performs all Grammars in the N.W in the important stats i.e points per A level and % of A levels that are facilitating subjects.Almost all go to Russel Group Unis. this yrs igcse results 90% A-A* with 60% at A*
The Grange is a relatively young school( by Indie standards) and has only a small endowment towards bursaries and only a few are offered compared to more established Pubic Schools like MGS/WGS
The biggest hidden cost is travel , some students commute from upto 25 miles away and transport costs can be upto £400 per term!You do not have to indulge in the expensive trips to California ect, most educational trips are day trips within the U.K
Anyway best of luck