"Getting the money out of politics" means reducing the influence of business and lobby groups. It may be true that increased advertising needs equates to more overall money being used, but certainly getting the 80% of uninterested voters involved will radically dilute the sway of the aforementioned groups.
I would also question the notion of that 80% being uninterested. The poor tend to be sceptical about changing their situation and don't see the point of voting. The young are less organised. For sure many non-voters are uninterested, but that doesn't mean that, were they forced to vote, they would not make somewhat informed choices that were in their own interests.