You really think £55mil or so on two more players is insane? Considering the money Utd will miss out on if they don't improve and the complete lack in quality in central midfield, with literally no defensive midfield options currently outside of a unreliable(fitness wise) Jones.
I'd be very surprised if Utd don't sign at least one more pretty decent player and I reckon it will be Vidal and then add in Blind for £15-20mil to bolster anywhere he's needed. CB, DM, wingback, fullback, seems a no brainer. How much is currently being spent per year on transfer in terms of, fee's being paid in instalments and in terms of FFP/on the books, amortised the existing transfer including Di Maria you're probably looking at £40-50mil a year, two more players costing about £50mil in total on 5 year contracts would take that to £50-60mil a year, considering the increased sponsorship deals and the potential losses in losing out on champions league for another season or two, £10mil a year over 5 years is nothing to Utd currently. They can cover that relatively easily.