Pep Guardiola has spent more than £1 billion on new signings during his managerial career so far.There's no doubt that Guardiola is one of the greatest managers of the 21st century. His success at Barcelona, Bayern Munich and now Manchester City, as well as his playing style and development of players, has seen him both reach and remain at the very top of his position.Pep Guardiola has spent an incredible amount of money on new signingsDespite Guardiola having won over 29 trophies to his name and a 74.25 win percentage during his 13-year managerial spell, he somehow still splits opinion.Much of that is because Guardiola spends huge amounts of money on new signings. He has certainly never been afraid to splash the cash in his pursuit to improve his team. Most of these expensive signings have worked out for him, while a few of them haven't.On that note, here's a look at the five most expensive signings that have been made by Pep Guardiola.#5 Aymeric Laporte - £58.5 millionAymeric Laporte's signing played a key role in Manchester City's Premier League success.The only January signing on this list, Aymeric Laporte arrived at Manchester City at the start of 2018.City were romping to the title that season, and were en route to the English top flight's first-ever 100-point season. But Guardiola wasn't fully convinced by his central defensive options, with Vincent Kompany no longer a regular.As such, Guardiola decided to sign Laporte by paying his release clause to his club and handing the defender his debut against West Bromwich Albion the next day.Laporte immediately became an integral part of City's defence, and emerged as one of the Premier League's very best defenders over the next 18 months. He was also named in the PFA Team of the Year in 2018-19 as Guardiola's team won back-to-back Premier League titles.So far the centre-back has managed to win three Premier League titles, four League Cups and one FA Cup during his time at the Etihad.5 + clean sheet ❌🚪 @JackGrealish Now time for international break 💪🏻 pic.twitter.com/2WSa1aMoi7— Aymeric Laporte (@Laporte) August 28, 2021The left-footer still remains an essential part of Manchester City's squad, but injuries have held him back over the last 18 months.#4 Riyad Mahrez - £61.02 millionRiyad Mahrez has been an incredible signing for Pep Guardiola.After playing a key role in Leicester City's fairy-tale Premier League success in 2016, Riyad Mahrez was one of the hottest commodities in Europe.But he didn't make a big-money move away from the King Power Stadium until the summer of 2018, when Guardiola, after seeing his team claim 100 points and score more than 100 goals, elected to add Mahrej to his attack.City broke their transfer record to bring Mahrej in, paying £61.02 million to make Mahrez the most expensive African player in football history.The electric Algerian winger has scored 40 goals and provided 38 assists in 146 appearances for Manchester City. He has produced several fine game-winning moments, including three of his team's four strikes in the Champions League semi-final win over PSG last season.Happy 30th birthday, Riyad Mahrez! 🎈One of Africa's finest 🙌 pic.twitter.com/z5v0BfuzqO— Goal (@goal) February 21, 2021Mahrez has made the right-wing position his own, of late, and is likely to remain a key player in that position for Pep Guardiola and City in the coming years.