Ask HN: What is the actual demand for niche job boards?

Trying to get some data points on what the actual demand is for niche job boards and would love some input from the technical recruiting world (if anybody here works in the that capacity).

1. Does anybody work in technical recruiting/hiring that can attest to the use of niche job boards for specific tech domains?

2. What do budgets look like for recruiters and what are companies typically willing to pay per post, per month, or per hire?

3. How do you learn about niche job boards? and why do you use the ones you use?