To chop or not to chop

[Sam1234]

Hi, a window installer wants me to have replacement window fitted in existing space, then fill the gaps with foam  and cover with finishing trims. This is instead of the recess being chopped out. He says it will save me money on a plasterer, which I accept, but is he just trying to make the job easier for himself? I guess the new  window might be a fraction bigger if plaster was chopped out but that might not make much difference to cost. It's replacement of a standard uPVC window with a uPVC sliding sash window if that is of any significance (we are now included in a conservation area).

[nod]

A plasterer for a day won’t break the bank

Im not keen filling up with foam and trims look cheap 

[Sam1234]

Thanks. He said £400

[Sam1234]

£400 extra for the plasterer. If no plasterer  £1250 for the replacement window