I put it through GPT a few times to get a best estimate
| Manager | Tenure | Net Spend (£ million) | 
|---|
| Roberto Martínez | June 2013 – May 2016 | +£47.7M | 
| Ronald Koeman | June 2016 – October 2017 | +£142.9M | 
| Sam Allardyce | November 2017 – May 2018 | +£8M | 
| Marco Silva | May 2018 – December 2019 | +£91.1M | 
| Carlo Ancelotti | December 2019 – June 2021 | +£5M | 
| Rafael Benítez | June 2021 – January 2022 | +£1.5M | 
| Frank Lampard | January 2022 – January 2023 | +£36M | 
| Sean Dyche | January 2023 – January 2025 | -£15M | 
 
Complete horror show from Koeman. Silva's looks worse than it is, as his Richarlison buy is effectively what gives Dyche his negative figure.