Kyle Walker for £50m. £50m for Kyle Walker. There is no way of saying it that does not sound a bit, well, odd.

That is not to do down Walker, who was probably the best right-back in the Premier League last season. But still: £50m for Kyle Walker.

In part it is to do with the changing role of the full-back. Gianluca Vialli used to say the right-back was invariably the worst player in a team, the one left over when the good defenders had been moved into the centre and the technically gifted players had been moved into midfield. Left-backs, being left-footed and therefore having a scarcity value, were somehow a different case, something exemplified in the way the first three great attacking full-backs were left-sided: Nilton Santos, Giacinto Facchetti and Silvio Marzolini.

That is not true any more. The full-back, even in a back four, has become an attacking presence and that means he must have not merely pace, stamina and defensive qualities but also the ability to beat a man and deliver a cross.

Walker can do all of that – even if there are some at Spurs who feel Kieran Trippier, who averaged 50% more accurate crosses per game last season than Walker, is the better deliverer of a ball. Having missed out on Dani Alves, a high-class, low-cost option, Walker is an understandable alternative for City; he has not won as much and he, to put it bluntly, is not as good a footballer, but he has Premier League experience. Whether he has the technical qualities to operate in that tucked-in, defensive midfield role Pep Guardiola often demands from his full-backs is debatable, which perhaps signals that City will return to a more orthodox understanding of the full-back role, but Walker will clearly be an asset to the squad.

But that does not address the central point, which is that he cost £50m, with potentially more to come in add-ons. Perhaps that is what the market demands but the market is coming increasingly to seem like an ass. Walker is only the latest of a series if extraordinary deals this summer: Romelu Lukaku for £75m, Alexandre Lacazette for £53m, Mohamed Salah for £37m, Jordan Pickford for £30m. It’s usually a cheap dig at football to point out how many hospitals or schools could be funded for a player’s weekly wage but, really, how are historians of the future going to explain a society that has dragged itself on under austerity for seven years and yet smiles benignly at a decent right-back going for £50m?

Timeline The final days of Mark Sampson as England manager Show Bullying claims emerge It emerges Eni Aluko, the England and Chelsea forward, made claims of bullying and harassment against Sampson and his staff in May 2016. An FA investigation, concluded in March 2017, cleared Sampson and his staff of wrongdoing but it emerges Aluko was paid a £80,000 settlement in a confidentiality agreement, which the FA insisted was to avoid disruption to England’s Euro 2017 campaign Aluko allegation Details become public of an allegation made by Aluko, claiming Sampson made a remark towards another player with 'racial and prejudicial connotations'. Sampson is alleged to have made reference to the number of times a player had been arrested Another Aluko allegation Aluko alleges Sampson made a racist comment to her before an England game. After telling Sampson she had relatives coming from Nigeria to watch the international, Aluko claims Sampson replied: 'Well make sure they don’t come over with Ebola' Sampson breaks public silence Sampson speaks publicly for the first time about the allegations and says his conscience is clear: 'This has not been a nice situation for anyone' A contradiction in evidence? Sampson appears to contradict evidence he gave to the inquiry when he tells a press conference he cannot recall ever having a conversation about Ebola with Aluko Drew Spence comes forward The Guardian reveals the FA is giving serious consideration to launching a new investigation into the Sampson affair after Drew Spence, one of two players to allege he had made a racial remark, comes forward to tell the governing body that what Aluko has said about the England women’s team manager is true Sampson sacked Football Association chief executive Martin Glenn becomes aware of the 'full detail' of inappropriate relations Sampson had with female players while he was manager of Bristol Academy

Even within football’s gilded bubble this is a deal that stands out. Walker is 27. He has only ever scored five goals (now, perhaps this is a sign that football has at last realised that goals are not the be all and end all of a player’s worth, but the point is that Walker is not merely far from being Lionel Messi or Cristiano Ronaldo, he is not even Stuart Pearce or Steve Nicol). He has won only 27 England caps (he may be the clear first-choice right-back now but a year ago no one would have been overly concerned if Roy Hodgson had preferred Nathaniel Clyne). And yet now he is the most expensive defender in history.

It feels as though a collective madness has gripped the Premier League, which now has the most expensive back five in history: Walker, John Stones, David Luiz, Eliaquim Mangala, Luke Shaw. In part it’s a result of the latest broadcast deal, which means that every one of the 20 Premier League clubs ranks in Forbes’s top 30 clubs in terms of annual revenue. And in part it’s because to the sheikhs, oligarchs and hedge fund grandees who own Premier League clubs, £50m is not actually that much money. The old scale, whereby a club’s wealth was in direct correlation to gate receipts and therefore had some grounding in the everyday world of fans, simply does not apply any more.

But still, the money has some value and if last season’s fall in viewing figures is a sustained trend, if Sky’s relaunch of its sports channels is a response to anxiety about the economic future, some of the transfer fees paid this summer could come to seem impossibly inflated.

In the early 17th century, the trade in tulip bulbs in the Netherlands reached unprecedented levels, particularly after the infection of some plants with the mosaic virus led to an exotic streaked effect on the petals. For years, despite warnings from guilds and the church, prices went up and up, seemingly without end until, abruptly, one day in February 1637, perhaps because of an outbreak of bubonic plague, buyers did not show up at a market in Haarlem. The bubble burst, the outrageous sums bulbs fetched suddenly seemed nonsensical and hundreds of investors were ruined overnight.

There is a danger always in being scandalised by transfer fees. Some of the reactions to Middlesbrough breaking the £1,000 barrier to sign Alf Common from Sunderland in 1905 look laughable now. The football boom has outlasted the financial crisis. Perhaps the sport’s internal economy is robust and these fees do make sense. Perhaps the Haarlem moment will never come. But on the other hand, Manchester City have just signed Kyle Walker for £50m.