In a capitalist world you're worth whatever somebody's prepared to pay - that's the elementary rule of supply and demand. But under what circumstances can Chelsea boss Jose Mourinho truly justify spending a record-breaking sum on prodigious Everton centre-back John Stones? A 21-year-old with just 44 top flight appearances under his belt that the Toffees will only surrender if the Blues decimate the Premier League's record fee for a defender, currently held by £32m Manchester City signing Eliaquim Mangala.

Right now, it's indisputable that Stones is not a £32m player. Even factoring into the equation the elevated price-tags that now accompany virtually every half-decent Englishman, it seems implausible a 21-year-old defender who has never made an appearance in the Champions League and thus far represented England on just four occasions can cost Chelsea the same as Diego Costa, a striker who arrived at Stamford Bridge last summer off the back of firing Atletico Madrid to a La Liga title and the 2014 Champions League final, with two national teams - Brazil and Spain - fighting over legitimacy of his services.

But in potential, style and situation, Stones is comparable to a young Rio Ferdinand, a hypothesis that to many makes Stones' £32m price-tag somewhat justifiable. No English centre-half had carried the ball out of the back with the eloquence and consistency of the former Manchester United stalwart until Stones broke into the Goodison first-team at the start of the 2013/14 campaign - a distinct defiance of stereotype that almost saw him claim a place in Roy Hodgson's World cup squad. Defensively too, the Toffees youngster is impressive; an expert attacker of the ball, averaging over one block per match last season, with the recovery pace to get himself out of self-inflicted trouble.

Likewise, Ferdinand was purchased by Manchester United for a massive £30m sum when he was 23 years of age and only just beginning to emerge as a regular for England. That remains the Premier League record spent on an English defender and the third-highest sum forked out for a Three Lions international - all the more impressively, during an era in which £30m truly felt like an outrageous amount of money. In today's terms, it converts to £45m.

Yet, the significant differences in circumstance are impossible to ignore. Ferdinand had already made 242 career appearances before moving to Old Trafford and United were forced to pay over the odds, having acquired him from bitter rivals Leeds United who, at the time, were one of English football's most dominant forces.

But, of course, these are entirely different times and the fact is market forces give Chelsea little room for manoeuvre. Right now, the transfer market is hardly overflowing with top quality centre-backs, which is why United have felt compelled to bid almost £45m for a 29-year-old in Real Madrid's Sergio Ramos, after deeming Valencia's Nicolas Otamendi poor value for money at £35m and being snubbed on several occasions by Borussia Dortmund captain Mats Hummels.

And that pool of centre-backs gets even smaller if your preferred type is young and English. Only five English centre-backs under the age of 23 featured in the Premier League last season; one of which was Stones, one of which plays for Manchester United, two of which joined their current clubs only last summer and the ultimate of which managed just ten top flight appearances.

Of all five, Stones registered the most outings at centre-back by almost two fold, and even increasing the age parameter to under 26, we're talking about a school of just twelve players - once again, five of which already play for top five clubs. Suddenly, we come back to the theme of supply and demand, further influenced by the not-so-capitalist principal of homegrown quotas, which FA Chairman Greg Dyke hopes to only make stricter over the course of the next few seasons.

In addition, Everton have the advantage over Chelsea around the negotiating table. They may be a smaller club but they're also under no pressing obligation to sell, having tied Stones down to a five-year contract in August 2014. The fact he's one of just two centre-backs currently in their squad has only amplified the Goodison outfit's reluctance, whilst the recent £49m sale of Raheem Sterling by Mersey neighbours Liverpool provides further evidence that their £32m valuation isn't as ridiculous as it initially sounds, at least in the context of the current transfer window.

So does that mean Chelsea can justify spending £32m on such an unproven player, forking out what will constitute Jose Mourinho's largest single spend since returning to west London two summers ago on potential rather than ability?

In my opinion, the Blues may as well wait until next summer. In that time, Stones can only further improve, making such a transfer fee seem like better value for money, or begin to stagnate, at which point Chelsea will have avoided a real transfer dud, but Everton's asking price is unlikely to change much from what it is now. How could it? It's already a monolithic valuation and the youngster's contract will be twelve months shorter. Likewise, if Chelsea sign a replacement for Atletico-bound Filipe Luis, they'll hardly be left short of defensive depth in the meantime.

But the Premier League champions, especially under Mourinho, have a knack of simply doing what needs to be done in the transfer market. They didn't mind spending £30m on Willian, £21m on a player they'd already signed once before in Nemanja Matic, or £18m on Andre Schurrle who - for better or worse - became a World Cup winner and a Premier League winner during his short spell at Stamford Bridge. I have no doubts over Mourinho's eye for a good player or what his squad needs - so if the 'Special One' views Stones as the ideal addition, he may as well go out and get him.