Mussolini attended the lectures at the University of Lausanne from May 1904 to July 1904 - a total of about ten weeks. There his presence was recorded at the courses of "political economics" (Pareto, but given by his substitute, Pasquale Boninsegni), "sociology" (Pareto), and "general philosophy" (Maurice Millioud).

As far as I know, we lack information about how involved with the courses he actually was. Given the short period of time, and the fact that he didn't complete any of the courses, it wouldn't be inconceivable that this brief education stint didn't really cost him much, if anything at all, besides any initial enrollment fee.

The bureaucratic needs to join the University of Lausanne for the summer session of 1904 are - unfortunately - something I don't know much about. I would expect them to have asked for some upfront payment, at least for clerical needs.

As to any such sum, Mussolini would likely have been able to put it together with his - not so regular - sources of income of his Swiss period. Historian Simone Visconti, who has recently studied Mussolini's experience in Switzerland during 1902-04, notes that

Whatever his economical situation, Mussolini always associated with the intellectual part of emigration […] The category of day laborers and construction workers, to which Mussolini later claimed to have belonged, was in truth the recipient of his political action […] They were the audience of his lectures, that he met on a regular basis, but weren't part of his daily routine.

His choice to attend some university lectures - as well as his longer and more extensive frequentation of the University Library of Geneva - would have played into his desire/need to acquire a modern and (as much as was possible for a socialist militant and emigrant) scholarly education.

This would appear as part of his mindset concerning education and its purposes, and his practical occupation/source of income as a public lecturer, correspondent, and writer for socialist newspapers such as the Avvenire del Lavoratore.

The socialist movement - even more so at the time - was hard-strapped for cash. As Secretary of the Stonemasons and Builders Union of Lausanne, Mussolini had earned 5 Francs per month (a worker would make about 100 Francs a month), so he had to provide with other paid "intellectual" work, as well as the occasional manual labor. During 1902-03 Mussolini would earn an additional 15-20 Francs per month, on average, for published pieces.

Given that this was just about the same as public assistance, there is no doubt that Mussolini had to rely on his activity as paid lecturer - usually in public debates, of limited intellectual scope, but enough to earn him a local reputation as a fierce polemical debater. It is the need to be up to date with cultural trends and topics that - paired with his desire to complete an "intellectual" formation - led to his frequentation of the Library in Geneva during January-April 1904.

By that time, Mussolini's reputation had grown - comparatively speaking - and thus, likely, his ability to command a decent fee for his lectures. His debate with pastor Taglialatela on March 25^th 1904 was followed by an audience of 450 people and earned positive reviews from both Serrati and the Swiss police, according to which Mussolini was "fort bien documentè".

His connections with Serrati - who had the ability to mobilize some financial resources, mostly in the way of providing work - might have helped him securing any funds he might have needed for his "documentary" searches.

Indeed it appears that Mussolini had been motivated to try attend the University of Geneva first, but had been prevented from doing so by his legal and political situation at the time.

It is not clear to me why this difference existed between the two Universities.

Hope this helps somewhat.