My take is that we have a limited budget with which to make all 4 signings and thought that we could get Perisic for about £35 million (which is probably around his market value if he was being transferred to another Italian club). Inter are playing hardball and we're now a bit stuck as overspending on Perisic would mean we can't afford our other signing. Perisic himself was probably seen as something of a 'budget solution' to allow us to spend big on Lukaku.
Hence Mourinho's recent comment about maybe now only being able to sign 3 of our targets.
Frustrating (if true) given that we are the most profitable club in the world, but I know many won't hear a bad word said about our owners...
I don't think so. Even if there was a budget set for "summer '17" which placed Perisic's value at, say £35m, I've never heard of any suggestion that the budgets cant be flexed a little bit and reconciled in subsequent windows.
I'd highly expect that, if the original budget didn't allow for an extra £10-15m in the first place, it would just be revised against subsequent transfer windows. Particularly as, in Jose's eyes, that £10-15m could be the difference between mounting a title challenge and not.