Salaries are definitely going up in the NBA. In 2005, Sloan was the 2nd highest paid coach and making only $500,000 more than Kerr. Today, he'd still crack the top-five, but that only assumes other coaches aren't given similar deals. A decade ago, ten coaches made less than two-million a year (with seven making a million). Today, zero coaches are making less than two-million a year. Jeff Hornacek, from what I can tell, is the lowest paid coach in the NBA at two-million exactly. No coaches in 2005 made more than $6.9 million (that was Rick Adelman's salary back when he coached the Kings - the highest in the league). Today, Stan Van Gundy and Doc Rivers both make seven mill.
The increase hasn't been dramatic, but the going rate for a head coach has inched up at least a million since 2005 (it looks like it was one-million a year back then). So, you can expect most rookie head coaches (sans the anomalies like Kerr) to make somewhere around two mill. Hollins would probably go for four-million with his resume.
Kerr seems to be the exception still, though, and most likely got that salary because he started a bidding war between two teams willing to pay out for a head coach they think can turn into greatness.
There are exceptions, of course, as Brad Stevens pulled in 3.6 million his rookie season. But two-million seems like a good starting point right now for most new coaches. It'll be interesting to see where it goes in five years since the trend is clearly going up (as it is in college sports, as well).