1) your $ goes much further in, say, Tennessee, than in New York. Making $150k in New York City doesn't get you very far. But making $180k in many parts of the country could mean a reasonably comfortable life. So it all depends on where you are and where you are going. Obviously the trajectory of future compensation is also a critical factor.
2) head hunters typically have contracts with employers who pay for HH's services. In my industry for example, typical arrangement for a mid level employee is 100% of the new hire's first year compensation.