Expenditure at top clubs is ALL about wages - transfer fees are not a huge deal.
United and Arsenal's net spend on transfers isn't that high (because they're adding to good squads and can sell players for good money) - but the wages they pay are huge and that's money that goes straight out of the club.
The approx £150 million net we've spent on players this year is described as a one-off, yet United and Chelsea pay a similar amount EVERY year in wages, with Arsenal and Liverpool not too far behind. I'd expect our wage bill to at least match Chelsea's in the next couple of years.
Chelsea talk about moving towards sustainability, but as soon as we have a big five someone will miss out on the Champions League and that's £25-£40 million lost in a year.