Jerome Bonaparte's suggestion was like a wake-up call for Georges Haussmann. All along, Haussmann had always focused too much on the theoretical aspects of renovation, never inquiring into the details of the renovation process.
Many specific issues regarding housing prices were delegated to his subordinates, who only provided him with the per square meter subsidy prices for houses in an area, after which he allocated funds from the City's finances. This certainly saved a lot of time, but it rendered Haussmann unable to control the intermediate stages.
If any mistake occurred in the intermediate stages, such as inflated house purchase prices, collusion between civil servants and landlords to inflate unit prices, or putting valuables that did not belong to them in the house to falsely claim it's their belongings, thus maliciously inflating purchase prices, the results would exceed the original estimates.
