This is touched in book Lenin A revolutionary by Christopher Read, Routledge, 2005. No numbers are given, though.

First, he earned some money by writing and giving lectures. Quoting Read:

Imperialism became one of Lenin’s best-known works. Ironically, one of the reasons he had written it in the first place, was that he was, as usual, desperately short of money.

As a functionary of RSDLP party he got a salary and his mother sent him money from Russia. She had state pension as a widow of a noble and also collected rent from inherited family estate. Russian government didn't interfere, they (indirectly) supported Lenin's faction in hope that his rigidity will destroy the party from inside.