My personal highlights:
> he cold called them with my resume
> Not even sure where he found my name in the first place
> I only became aware of this company via this recruiter
> His finder's fee is very high, and it wasn't disclosed until after the interviewing took place.
This sounds like one of those LinkedIn/Dice recruiters who messages/emails you out of nowhere trying to pressure you into a job for their precious "finders fee". Also, the recruiter seems to have not had any prior contact with the company before and is trying to pressure the both of you into payment.
IIRC, this is why most job apps have "NO RECRUITERS" in big bold print on the applications. I'm surprised that the employer even offered to interview you knowing that the recruiter cold contacted you both.
> They never signed an agreement with the recruiter in the first place, he cold called them with my resume. Likewise, I never signed any agreement with this recruiter.
This is the most important part. If nothing was signed, then nothing can be truly enforced. So OP/the company could get away with not talking to the recruiter anymore since there's nothing to enforce payment of the finder's fee. That being said, the recruiter could become very evil if he/she finds out his payment isn't coming (threatening, even).
I personally spent a year out of work after college and learned the hard way just how low the bar is for someone to call themselves a technical recruiter. After creating an account on Dice, I was called daily for months about "technical opportunities" by recruiting firms with hastily put together websites and disconnected phone numbers (as well as the occasional McDonalds as their listed address). Now that I'm on the job market again, I'm having to be very careful about what sites I use and what information I leave online.
Bottom line about OP's situation: RUN AWAY. Although it is legal for you to cut him/her off since nothing was signed, the scammer (let's call this recruiter for what he/she really is) would probably start threatening OP, the employer, and their respective families. This guy is nothing but scum, and is a huge reason why people have trouble finding good jobs. The fact that you were actually interviewed is also a red flag since it illustrates that the company has no idea how to handle these sorts of "recruiters". It's possible that they're trying to be nice to you. But, based on personal experience, they're usually hiding something as well (but that's another story for another super long HN post).
TL;DR: Both OP and the employer are being scammed. OP needs to run away now before it gets worse.