You do not need to pass the ATPL exams but you will need to pass the CPL exams to complete the kind of instruction that you describe. Since, I assume, you hold at least a CASA and/or FAA CPL(A), with the experience you describe the flight training required for an EASA CPL(A) under the UK alternative means of compliance is a minimum of 7 hours. Even combined with the instruction required to pass the arcane EASA theoretical knowledge exams, it is difficult to see how this could be worth anything close to $24k.
Conversion of your FI certificate under the same AMC will require a minimum of 15 hours of flight instruction and 30 hours of ground instruction.