Somewhere between $10K and $30K per hire. They only get paid when we hire people they bring us. Some recruiters manage to negotiate recurring fees but I have nobody working under those terms at this time.

Recruiters try to build systems more robust than cold-outreach on LinkedIn but most of my hires in the past year have come from cold-outreach tactics. They have databases of candidates but most of that database isn't actually interested in a new job at any given time and it's as productive to work the database as it is to work LinkedIn unless the recruiter has a friendly relationship with a specific candidate. Regardless, you can't sell a candidate to multiple employers in any given 1-2 year period so you always need new candidates anyhow.

If I had more free-time I would totally try doing this myself. The hardest part is getting HR to let you recruit for their open roles.