Top-performing sixth-form colleges get up to four students through three A-levels for every one success achieved by neighbouring private schools on the Assisted Places Scheme, it shows.
The study compares costs published by the Further Education Funding Council with local management of schools data and advertised fees (including the Assisted Places cash) from independent schools.
However, the study by a group of sixth-form college principals goes further than looking at raw costs. It ranks overall college inspection grades with the positions achieved in national league tables. It then compares the top colleges locally with the best from the other sectors in the area.
By comparing like with like, the principals insist they have shown recent Department for Education and Employment research into costs to be flawed. The DFEE argued that when comparing like with like, the differences between schools and colleges all but vanished.
Kevin Conway, principal of Greenhead College in Huddersfield, said: "Glaring examples can be found all over the country of student funding which is giving poor value for money for the taxpayer in one sector and outstanding value in another."
Comparing the best in West Yorkshire, his figures show that while assisted places in Bradford, Wakefield and Leeds, including Bradford Grammar School, cost around Pounds 4,428 a year, nearby state school places cost Pounds 3,546. But students gaining comparable grades at his college cost Pounds 2,627.
The 14-page analysis was being sent to all political parties as The TES went to press. Dr Conway said: "We want answers from them all. What will they do to remedy these clear discrepancies?" It was no good their talking about selective schools being more deserving, he said.
"We do not select in the same way as the highly-selective schools. We have a broader ability intake and yet when you compare their results with ours then ours are just as good if not better."
Hills Road College in Cambridge came top of the league in his analysis of inspection grades and league table achievement. But it cost just a quarter of the fees charged in neighbouring private schools.
The college principals were quick to point out that they had not skewed their analysis towards low-spending colleges. This was a claim cited by some politicians following earlier efforts to highlight differences in spending.
Seventeen of the top 30 colleges analysed in the study spend above average on the Further Education Funding Council scale of college costs. All except for two of the rest are very close to the average.
Dr Conway said: "The current spending estimates by the Conservative Government have indicated cuts of around Pounds 400m by the year 2001, when the latest round of cuts and efficiency measures for the next three years are added up."
He was concerned that unless Labour was pushed hard, it would avoid any commitments to remedy this.
Sixth-form colleges are angry at being hit twice financially. First, when taken out of local authority control, they lost the chance for extra cash and grant-maintained status. Then their cash was cut by 35 per cent per student over three years, 5 per cent worse than other colleges.
John Guy, principal of The Sixth Form College, Farnborough, said: "There is a clear need to level the post-16 playing field. Whatever rates of spending we decide for adult education generally, we cannot go on funding 16-19 education in the way we do."
Colleges giving equal value to the top independent schools, and often at a cheaper rate, are Greenhead, Hills Road, Sir John Deane's in Nantwich and King George V in Southport.
A group of principals recently lobbied FEFC chief executive David Melville over the latest Government decision to axe Pounds 115m in growth cash. Some will be very hard hit with the likely national shortfall of 256,000 FE places as a result of the cuts this autumn.