God, let's hope nobody ever tries that. Higher prices because you don't consent to more invasive tracking, because it poses a higher fraud risk to the company.

Thankfully, processing the same data for fraud prevention should be a different consent process/option than processing it for targeted advertising.

That's kinda the point.
Any server you connect to knows your IP address. As does any equipment between your home network and the remote server. It has to, that's how networks work.

Processing that to ensure your IP isn't abusing their servers is legitimate interest.

Processing that along with your interactions with their website likely isn't legitimate interest, so has to get consent (as this is likely profiling or user tracking, regardless of cookies used)

You could argue that it is legitimate interest, but then you have to back it up in your privacy policy as to why it is required, and it could be easily challenged as it's such a broad and subjective term (whether that challenge goes anywhere is up to enforcing bodies, like the EU/ICO/whatever).
The idea is that the barrier of entry for "legitimate interest" is high enough and that abusing legitimate interest carries a risk, so that it isn't the default.

Just because you have access to the data, doesn't mean you can use it however you want.