We need at least 340 million in 4 years for this signing to happen (100 million transfer fee, 240 million for salary).
Almost a third of that sum, 105 million, we can get by selling Higuain to Chelsea (60 million tranfser fee, 45 million for salary).
Through those 4 year we will surely get a third of that sum just from the marketing boost.
The rest, IMO, can be financed through other incomes over the years.