A joint study by the five major FE associations challenges controversial data produced by the Department for Education and Employment comparing the cost of three A-levels and of vocational qualifications in institutions.
The college bodies, which have disputed the DFEE figures since a first draft was published last December, claim key factors have been left out of the calculations, skewing the results to make colleges seem more expensive.
Their alternative version, which takes account of the missing elements, suggests the DFEE has overstated the cost of three A-levels in a general FE college by Pounds 540 and Pounds 285 in a sixth-form college.
The colleges have also compared the costs of a level 3 national vocational qualification for a student in a college or a trainee on a training and enterprise council-funded programme with a private provider. They calculate that colleges can provide the training considerably more cheaply.
The DFEE is now formally seeking responses to its third and final set of calculations. The second set, which were never published officially but were leaked to The TES, placed grant-maintained schools as the most costly provider of three A-levels - a position that is taken by sixth-form colleges in the final DFEE version.
The colleges' new document says the associations are unconvinced that the department's work so far gives a "fair and objective view". They acknowledge some "weaknesses have been corrected", but claim errors remain.
They insist the calculations, despite revisions, do not take sufficient account of different prior attainment of learners coming to schools and colleges, nor of extra-curricular activities. They also suggest choosing three A-levels gives an incomplete picture.
The associations say the calculations do not give full weight to the effects of capital funding changes on colleges. They also object to the DFEE's comparison of TEC-funded NVQs with college-taught general national vocational qualifications.
The department's costing of TEC-funded programmes does not take account of the cash input from employers, so does not give a full picture of resource costs of training, says the new analysis.
The Further Education Funding Council is to challenge the DFEE calculations. A spokeswoman said: "The council is not convinced of the basis of the costs. "