How does money flow in MN politics? Some of it is traceable. Some of it is not. MN law requires people being paid to lobby to register with the MN Campaign Finance & Public Disclosure Board (but not specify the exact amounts of money). MN law requires full disclosure of all campaign contributions. But in my view, the limits on contributions made directly to candidates are low and not that meaningful. [I don't think you can buy a legislator for $250.]
However, the traceable money starts to get interesting if you spend hours pouring over Board reports and look for who wants what and add up the amounts of these individual contributions, particularly the contributions made to political committees.
One big source of untraceable money is what is paid to public affairs consultants who are not registered to lobby. Another is who, exactly, is paying for interest groups who are lobbying the public, not the legislature.