Chelsea have been one of the biggest spenders in the transfer market since billionaire owner Roman Abramovich took control of the club in 2003.Abramovich’s money coupled with his ruthless yet successful approach to hiring and firing managers, has helped put Chelsea on the map as one of the biggest clubs in world football.The Blues have spent huge sums of money on various players across the globe. Most recently, Chelsea broke their transfer record to bring Romelu Lukaku from Inter Milan for £97.5 million. In addition to that, the Blues had also spent close to £200 million last season to strengthen their squad.Chelsea's most successful players have arrived at a bargainWhile Chelsea continue to spend big in the transfer market, a quick look into their history tells us that the Blues' most successful players have come at a bargain. Most of these players arrived at the club for next to nothing but made a huge impact at Stamford Bridge, proving themselves to be some of the best in their position.Without further delay, let's take a look at the five greatest bargain signings in the club's history:#5 Frank Lampard - £11 millionFC Bayern Muenchen v Chelsea FC - UEFA Champions League FinalAlthough £11 million was quite a bit of money back in 2001, Frank Lampard enters this list purely because of the service Chelsea got from the midfielder for that price.The England international went on to become the club's highest ever goalscorer, with 211 strikes during his 13 years at Stamford Bridge. He scored several crucial goals during his time at the club, including a brace away to Bolton Wanderers in 2005 to seal the Blues' first league title win in 50 years.Lampard was one of the few who managed to win every possible trophy at the club. He won 11 major titles at Chelsea, which included three Premier Leagues, one Champions League, one Europa League, two League Cups and four FA Cups. He also managed to win the FWA Footballer of the Year award in 2005 and finished as the runner-up for the Ballon d'Or in the same year.Hugh Dickson@hd_hugh"@Squawka: Frank Lampard: Chelsea career in numbers. #CFC http://t.co/xclF4p0ijn" Cant argue with those stats,!!!!!!!! #legend3:36 AM · Jun 3, 2014"@Squawka: Frank Lampard: Chelsea career in numbers. #CFC http://t.co/xclF4p0ijn" Cant argue with those stats,!!!!!!!! #legendLampard's managerial stint at the club didn't turn out to be as successful. However, he will always be loved and adored by the Chelsea fans and rightly so.#4 Gary Cahill - £7 millionChelsea FC v Watford FC - Premier LeagueGary Cahill was deemed to be just a squad player when Chelsea signed him from the troubled Bolton Wanderers in January 2012. However, Cahill turned out to be one of Chelsea's best signings in the last decade and was a crucial player for the Blues in defense.The Englishman immediately slotted into the center of Chelsea's backline and was pivotal to the team winning their maiden Champions League title just four months after his arrival.He further went on to win two Premier League titles in 2015 and 2017 and also became Chelsea's captain after John Terry's departure. The 35-year-old's time at the club came to an end in the summer of 2019 after the end of his contract. He now plies his trade with AFC Bournemouth in the Championship.₁₀🇫🇷@DebbyChelsea10Gary Cahill at Chelsea 2x Premier League2x FA Cup2x Europa League1x Champions League 290 Appearances24,675 Minutes25 goals Best January signing in the history of PL12:32 PM · Jan 30, 20211567192Gary Cahill at Chelsea 2x Premier League2x FA Cup2x Europa League1x Champions League 290 Appearances24,675 Minutes25 goals Best January signing in the history of PL https://t.co/PhlBdTiu0pCahill has been a vital part of Chelsea's success over the last decade and remains an absolute bargain whichever way you look at it.