Individual humans can only contribute up to $2700 directly and $5000 to a PAC. Corporations are not tied to these limits if they want to establish their own PAC which is what they do. No one will prosecute PACs that blatantly collude with candidates illegally so campaign contributions to PACs are essentially limitless for corporations but not for people. People have less rights to speech than corporations. The problem is that corporations and lobbying groups are legally allowed to buy influence and more money is more influence so the wealthiest people and businesses will always have more rights under our current system as long as they keep the masses divided.
Edit: Source: https://www.thoughtco.com/current-political-campaign-contrib...