To illustrate, here's data on the total cost of elections to the candidates from the ever-useful Center for Responsive Politics its Open Secrets website. The yellow bars show costs of Congressional elections, while the green bars show costs of presidential races. Thus, this year's election will cost Congressional candidates about $5 billion, while the total cost of the 2016 Congressional and Presidential campaign was more like $6 billion.
But the bigger issue is that we can see pretty clearly what campaign spending goes for: advertising, mailing, travel appearances, and so on. That spending needs to be disclosed and accounted for. Contrary to what a lot of commentary seems to imply, campaign contributions are not personal income to politicians. In contrast, spending on lobbyists is cloaked in mystery. The amounts spent on lobbying are supposed to be disclosed, but what precisely is included in lobbying is often not very clear. The activities of lobbyists, and in particular how they influence or even just write the fine print that affects their employers, does not happen in public. The effects of lobbying are typically not known or disclosed.
From the Open Secrets website, here is spending with officially registered lobbyists, which is almost certainly a substantial understatement of total spending on activities that bear a strong resemblance to lobbying. (For example, corporate charitable contributions are often given in a way that seems designed to exert political influence.)
I do worry about whether the low and emotive campaign ads I see, from all sides of the political spectrum, have much effects. Are the people who write and place such ads really understanding what moves voter turnout or voting decisions? But that said, the lobbying that I don't see seems to me a more serious issue for what ends up being written into laws and rules.