The problem is not the fee (who seems stabilizing themselves around the 20-30m mark) but the salary. Someone with a 150k a salary will cost the club more then 7m a year or 36m in 5 years. That's a big sum of money, expecially considering that by signing someone with that sort of salary you risk of having players coming to SAF's office asking for a pay rise.
I think that SAF's plan is to buy time. He will keep his old guard as long as he can to allow the current crop to grow old enough to replace them. If this plan fails then SAF will have to buy big but he won't turn to plan B unless he is certain that plan A has failed. Any talent that we will bring will probably be a promising player in Defour/Henderson mould.
The only exception to the rule may end up being the goalkeeper's department.