The amount of money police forces in England and Wales receive from drivers attending speed awareness courses has jumped by almost a third.
Figures obtained by the Press Association show that the contribution a constabulary gets for each person it sends on a course leapt from £35 to £45 last month.
The money is designated as a cost recovery fee to reimburse police forces for the expense involving in catching speeding motorists.
With around 1.2 million drivers attending speed awareness courses annually, police forces will now collect £54 million each year.
Forces receive millions of pounds more from the 200,000 road users attending the several other courses run under the National Driver Offender Retraining Scheme (NDORS) umbrella.
NDORS courses are provided by private companies on behalf of the police.
Courses may be offered to offenders at the discretion of police forces and attendance means offenders will avoid penalty points on their licence and a fine.
Analysis of course costs shows huge differences in what drivers can expect to pay depending on where they live.
Speeding motorists attending courses in Northamptonshire pay £75, while those attending in Essex will pay 32% more (£99).
The cost for motorcyclists attending Ride courses, part of NDORS, are even more variable, ranging from £80 in Lancashire to £185 in Norfolk and Suffolk, a £105 difference.
Steve Gooding, director of motoring research charity the RAC Foundation, said: "Most people attending speed awareness courses sing their praises but what they might not realise is the postcode lottery they face in terms of the costs involved.
"Surely there is no other part of the criminal justice system where fines and penalties vary by as much as a third across the country?
"Intuitively, people would expect to pay a fixed price for doing wrong, not an arrangement that offers rewards for shopping around or penalises partly because of where people live."
A spokesman for NDORS said course providers tried to absorb as much of the 29% rise in the police cost recovery fee as possible, meaning speed awareness courses went up by an average of less than one pound last month to £88.90.
He said the increase in the money forces receive was "in line with Treasury requirements". The charge was previously unchanged since 2010.
Pricing of courses is a "complicated issue" due to differences in the number of attendees, locations and durations, the spokesman added.
Figures showing the areas with the most and least expensive courses - and the average cost - were provided by NDORS without a full nationwide breakdown.
A National Police Chiefs' Council (NPCC) spokesman said: "The NPCC has helped to implement new arrangements for the funding of driver retraining courses which are transparent and accountable.
"Police forces do not profit from these courses and the financial model provides for cost recovery only."