The 2021 summer transfer window saw a number of the Premier League's biggest clubs splash the cash to sign some of the hottest properties in world football.Manchester City spent £100 million, thereby breaking the British transfer record, to sign Jack Grealish from Aston Villa. Chelsea spent the second-highest transfer fee in Premier League history to sign Romelu Lukaku (£97.5 million) from Inter Milan.Manchester United spent in excess of £100 million to sign Jadon Sancho from Borussia Dortmund and Raphael Varane from Real Madrid. Arsenal have surprisingly been the biggest spenders of the summer transfer window thus far, having spent £130 million.The coronavirus pandemic has negatively impacted most clubs in world football, which has forced a number of teams to curb their spending. The focus has shifted to selling fringe players and some of their highest earners.The likes of Liverpool and Tottenham have been wary of shelling out large sums of money on transfer targets, and have focused on spending wisely this summer.Meanwhile, the likes of Everton, West Ham United and Leicester City have focused on completing bargain deals for players who have the potential to develop into stars.Over the years, some of the biggest clubs in the Premier League have signed players for bargain prices. These players have gone on to have a huge impact on their clubs and have become legends of the Premier League.On that note, let's take a look at the 5 biggest bargains in Premier League history.Bargain buys who lit up the Premier League#5 Vincent Kompany, Manchester CityBrighton & Hove Albion v Manchester City - Premier LeagueManchester City signed Vincent Kompany for an undisclosed fee from German club Hamburg in the summer of 2008. After struggling to adapt to the Premier League in his first few months with the club, Kompany soon became an integral member of the club's starting line-up.He was one of the first signings of the Sheikh Mansour era, and turned out to be one of the biggest bargain signings the Premier League has ever seen. The Belgian captained Manchester City to four Premier League titles during his eleven seasons with the club.Kompany made 360 appearances for the club in all competitions and scored 20 goals. The former Manchester City captain firmly established himself as one of the best centre-backs in the world during his time at the club.Vincent Kompany made his @ManCity debut on this day in 2008 💙 pic.twitter.com/KeUsdTA9Bx— ManCityzens (@ManCityzenscom) August 24, 2021The club was forced to spend in excess of £150 million on the likes of Ruben Dias, Aymeric Laporte, and Nathan Ake in a bid to replace Vincent Kompany. Kompany left the club in 2019.#4 Andrew Robertson, LiverpoolWest Bromwich Albion v Liverpool - Premier LeagueAndrew Robertson's move from Hull City to Liverpool in the summer of 2017 in a deal worth £8 million was one that baffled many as the Reds were in desperate need of a top-quality left-back. Robertson had failed to impress during the 2016-17 campaign whilst playing for Hull City in the Premier League.The Scottish left-back has, however, developed into one of the best of his generation during his time there, and has reinvented the concept of an 'attack minded' left-back.Andy Robertson became the fifth senior player in recent weeks to commit himself to Liverpool when he signed a new long term contract on Tuesday.https://t.co/yd59AccX4F— Sportstar (@sportstarweb) August 24, 2021His workrate, crossings, set-pieces and ability to score goals on occasion make him one of the best full-backs in Europe at the moment. The 27-year-old played a pivotal role in Liverpool's Champions League triumph during the 2018-19 season, and helped the club win its first ever Premier League title in the 2019-20 season.