Let us begin with Fernando Torres.
Via BBC Sport, Chelsea paid Liverpool £50 million for "El Nino" Torres in 2011 and the experiment has been a relative disaster. The mitigating circumstances surrounding the Spaniard's performance in west London vary but—suffice it to say—Torres has come nowhere close to meeting his lucrative price tag.
Scoring 44 goals from 166 appearances, the (oft) Spanish international has seen the form he enjoyed in his youth and at Liverpool dissipate.
In a certain respect, Chelsea's 2011 January window did nothing but stifle the growth of Daniel Sturridge (who ironically left for Merseyside) and Romelu Lukaku (currently in Merseyside); not to mention, Roman Abramovich essentially funded the Reds' acquisition of Luis Suarez (and Andy Carroll).
The alleged sum you ask?
Hence you might realise why Costa seems a case of: "Once bitten, 50 million times shy" to many of the Stamford Bridge faithful.
The Brazilian-born Spanish international has been rampant in La Liga, scoring 34 goals in 44 matches. As such, his value has accelerated like Usain Bolt out of Olympic starting blocks. The worry becomes Costa is a one-year wonder, but Chelsea have had marked success with perceived "flash-in-the-pan" strikers before.
The closest comparison for Costa is Didier Drogba.
In 2003-04 France's Ligue 1 was torched by the Ivory Coast international. The irrepressible forward logged 30 goals in 50 appearances for Olympique de Marseille (l'OM) and led his squad to the UEFA Cup final (now the Europa League).
l'OM purchased the Ivorian from EA Guingamp in 2003 for £3.3 million; after one campaign at the Stade Velodrome, Drogba's value had multiplied over seven times.
Jose Mourinho, then FC Porto boss, played against l'OM in the 2003-04 Champions League group stage and spotted Drogba. When the Special One was recruited by Abramovich to manage Chelsea in the summer of 2004, the Ivory Coast captain made his way from Marseille to London in one of the Portuguese's first initiatives as boss.
And the rest—as they say—is history.
Leading toward the question: Is Costa, 25, worth (for the same position, physique, mentality and manager) £19.3 million more than Drogba, 26, was in 2004?
All Chelsea supporters would agree Drogba was the best outcome possible for a £24 million striker; the return the Ivorian gave Stamford Bridge might have been worth upwards of £60 to £70 million—but the phrase "20-20 hindsight" comes to mind.
The transfer market is an animal.
Gargantuan purchases like Real Madrid's acquisition of Cristiano Ronaldo (£80 million, via BBC Sport) can pay dividends, likewise bargain buys, such as Chelsea's 2004 Petr Cech capture (£7 million, via Chelsea FC), can be just as clinical and/or pivotal.
By the same token, football's transfer market can be ruthless. From the Abramovich era—Adrian Mutu, Andriy Shevchenko, Yuri Zhirkov and Torres are the tip of the proverbial iceberg of recent transfer flops.
Not to suggest Costa is heading towards their infamous company, but the idea that paying £50 million for a player will somehow fix Chelsea's lack of goalscoring is rather simple-minded. Success or failure resides with choosing the right player, not the amount of capital one spends to acquire them.
Mourinho knew at the beginning of the season his strikers were going to be problematic. The Wayne Rooney saga, Lukaku's loan to Everton and Samuel Eto'o escaping Russia with Willian, all per BBC Sport, as evidence. Therefore, it stands to reason the Chelsea boss will attempt to remedy the only glaring concern with his squad.
Torres, Eto'o, Lukaku and Demba Ba, per David Kent of the Daily Mail, have been linked with exits this summer. The scenario could play out where Mourinho has just one striker on the Chelsea books come the World Cup. With a transfer kitty boosted by sales and wage relief, the possibilities are seemingly endless.
Yet there is something about the figure "£50 million" which screams desperation.
All things being equal, the Blues are three wins away from John Terry hoisting the European Cup and one Manchester City slip from having the Premier League title race in their hands. Not a bad season for Chelsea—you look to Old Trafford, The Emirates or White Hart Lane and think: "Could be worse."
To answering the title question: "Is Atletico Striker and Blues' Target Diego Costa Worth £50 Million?"
In two words or less: Fear.
Clubs worry if they fail to rock the boat with enormous sums of cash, the opportunity to acquire the player will pass.
If Mourinho really wants Costa as badly as the papers would make it seem, he has the perfect opportunity to get the job done next week. When Chelsea visit Madrid on 22 April, the Portuguese needs to flex his silver tongue, which has lured the services of many before and convince the striker Chelsea is where his future lies.
If the player wants Chelsea, as we have witnessed with Eden Hazard or Kurt Zouma, the deal gets done—without exorbitant wastes of both cash and energy.
All that said, would Costa's fee be ridiculously high?
Will he be a Chelsea player come August 2014?
Will he be the next Drogba?
If another one exists, west London would surely welcome him aboard but as William Shakespeare told us in All's Well That Ends Well:
Oft expectation fails and most oft there
Where most it promises, and oft it hits
Where hope is coldest and despair most fits.
In short, Shakespeare meant: "Don't get your hopes up too much; football—and strikers especially—have a way of making us all miserable."