Arturo at Wages of Wins recently posted a free agent cheat sheet which you can find here. This chart ranks players from top to bottom based on their expected salary according to their average wins per 48 minutes (WP48) over the past three seasons and their projected WP48 over the next 4 years based on the typical career trajectory of a player at the respective position.
Keep in mind that a WP48 of .100 is roughly average, and that most players tend to plateau around age 25 and typically do not make significant strides past that age. This spreadsheet sets the value per win at $1.47 mil, and for the more mathematically inclined you can read about the methodology for calculating WP48 here.
I know a lot of people here are already very well versed in these metrics but here it is for the layman. The bottom line is that a player who scores a lot of points while using few possessions while defensively holding their opponent to few points over many possessions will have a higher WP48. It's worth noting that calculating the defensive statistics is much more subjective because of what information is actually available in the box score.
Basically, Arturo took the projected calculations for WP48, multiplied by 82 games, multiplied by the fraction of minutes that player actually played, then multiplied by $1.47mil to arrive at the fair value for that player.
More on Batum below the fold:
For the linked sheet, Wages of Wins used this equation to calculate fair contract value: Projected WP48 * 82 games * Fraction of Minutes played * $1.47 million = Yearly Contract Value
Since Batum played roughly 47% of the available 48 minutes he could play on average, WoW calculated his per year value like this: .198 (WP48) * 82 games/year * .47 * $1.47 mil = $11.19 mil/year. So, if you put a lot of faith in the WP48 metric, then you should be relatively happy about the contract offer the Wolves made to Batum especially considering that he will likely average much higher than the 23 minute per game used in the above calculation.
Now obviously the main arguments against this are 1. You think WP48 is a bad metric 2. You don't value wins at $1.47 million per win or 3. you don't believe Batum will have a typical career trajectory and has already hit his plateau. All of these are reasonable arguments, depending on what evidence you bring to the table, but the bottom line is that the dollar value being offered for Batum is not really as outrageous as many people seem to think it is.