Hiring itself and losses from going without are very expensive, I find it weird that any company wouldn't rather retain. I wouldn't ever be surprised that hiring cost $10k all up.
If a company only used external recruiters for any position above 100K it's going to cost them 15K+. More likely 25K. Now if they try on their own as well by posting jobs, hiring internal recruiters, network... Hiring is expensive.
Recruiters take up to 20% of first year salary or more plus the time to retrain, a 10k dev is a cheap one.
In Chicago, some recruiters have started asking for 30%. I've refused to work with these companies but rates are definitely going up.
London here. Thought it was 10-20%
I asked a recruiter that placed me and he said he's usually taking 20-35% :D