Lobbying is a symptom of the problem that the federal government has way too much money to hand out to various states, corporations, industries, government programs, etc. The federal government as described in the Constitution should be orders of magnitude smaller than it is now, and should have orders of magnitude fewer funds to disperse.

Lobbying itself shouldn't be illegal, it should just be de-incentivized by controlling the federal government's size and scope per the Constitution. This would also fix a lot of the corruption among federal representatives, who all too often are judged for the amount of booty they can bring back to their states.