I posted a related graph showing average team payroll alongside the payroll for the champion, see Average Team Payroll vs. Championship Team Payroll (Adjusted 2013 Dollars). This chart shows the highest and lowest payroll teams each year from 1990-2012, with dollars adjusted to 2013 dollars to account for inflation.
The graph shows how in the early 90s there was parity among team spending, but that diverged starting in the late 90s and especially in the mid-2000s, where you had teams funded by billionaires (Paul Allen and James Dolan) for whom money was not an object, compared to teams that were making bank on the luxury tax and putting out an inferior product (hello Donald Sterling and Bob Johnson!). The most recent CBA aimed to fix this disparity, and I think we're seeing the results.
For more on NBA salaries, see two of my previous posts - All Paid NBA Team and Real and Nominal Average NBA Salaries: 1985-2013.