The Met has spent almost £8m investigating allegations of wrongdoing involving journalists over the last year.
New figures obtained by Press Gazette also reveal that more than 150 staff have been working on the various probes.
Operation Weeting – the Met's second investigation into phone-hacking – has racked up £5.9m in costs since its launch in January 2011 to the end of 2012, using 83 officers and 19 administrative staff.
Operation Elveden, the probe into illegal payments to police and public officials, has so far cost £1.5m and employed 36 officers and nine staff.
A further £0.4m was spent on Operation Tuleta, the inquiry into computer hacking, involving seven officers and one administrator.
These are the Met's forecast costs for operations up to 29 February 2012 – but the final figures are likely to be higher as they do not include legal costs.
Press Gazette has also obtained projected costs from the Met over the next three years for the three operations, along with that of Operation Appleton, the force's response to the Leveson Inquiry.
The estimated budgets for the four operations are £14.2m in 2012/13, £10.9m in 2013/14 and £6.1m in 2014/15 – totalling £31.2m.
The figures for January 2011-February 2012 were obtained under the Freedom of Information Act by freelance Garth Pearce, who passed them on to Press Gazette.
Pearce said he was concerned that the 'endless Leveson Inquiry is politically motivated to curb the power of a UK free press", adding: 'I predict it will be judged as the most useless inquiry in British peacetime."
Last week the Government announced that the Leveson Inquiry has so far cost taxpayers £3.2 million – and the total cost for part one of the investigation is expected to reach £5.6 million.
News Corp's own investigation and legal costs incurred by hacking and bribes have so far cost the company well over £100m.