Don't forget that many of the colleges had scholarships for the "poor, stupidly bright" kids going back several centuries: the Oxbridge colleges had traditional links with different areas of the country going back surprisingly far in history. For example, writing of Merton (Oxford, founded 1264) "By 1370 the college had been converted to a predominantly monastic society, but by 1384 arrangements were made for the maintenance of five poor secular undergraduates who were to assist in the chapel and who were to act as servitors to the monk-fellows. After achieving competence in grammar, these poor scholars were to study arts and one or two of them might even proceed to civil law." [1]
Whilst it is undeniably true that the predominant occupant of an Oxbridge college was a comparatively well-to-do member of society, I suspect that the disparity of fees mentioned reflects the disparity of charges made at the time.
[1]: The History of the University of Oxford: Volume II: Late Medieval Oxford by J. I. Catto and T. A. R. Evans, Print ISBN-13: 9780199510122
Whilst it is undeniably true that the predominant occupant of an Oxbridge college was a comparatively well-to-do member of society, I suspect that the disparity of fees mentioned reflects the disparity of charges made at the time.
[1]: The History of the University of Oxford: Volume II: Late Medieval Oxford by J. I. Catto and T. A. R. Evans, Print ISBN-13: 9780199510122