He's a restricted free agent. Spurs will match any reasonable offer, and the most he can be offered in year one is about $5.6 million.
They will likely be trying to clear cap room to go after Durant. And even if he's not ready on offense his rebounding blocks and steals are great. And he is being held back because of these guys named Duncan, Aldridge & David West.
His cap hold is all of $1.44 million. While it's possible that will matter, it's unlikely. And they pretty much only get Durant if Duncan retires -- they need to get $20 million in salary from somewhere, and that somewhere has to be a couple of retirements, such as Duncan.
Agree to disagree, mate. Per Marc Stein's most recent article (he's the only guy for ESPN basketball that I trust), the Spurs would be looking to move Danny Green, Mills, and Diaw, and they'd also let Boban go. Then Duncan and Ginobli and maybe even west opt out and then re-sign at even further discounts.
Boban will cost them all of an extra $900k against the salary cap (because of the minimum roster holds). If they're willing to let Boban walk for that little, that should tell you what the best organization at scouting talent thinks of him. If they actually trade all three of Green, Mills, and Diaw, they'll have enough to sign Durant without Duncan and Ginobli taking paycuts. And West is already scheduled to make the minimum, so he can't take a pay cut (although he can sign a one-year which saves the Spurs cap space but pays him the same amount).
But the Spurs could find the money to pay Boban in a world where they trade those three for Durant. His salary is pocket change by NBA standards. So either they think he's barely worth the minimum, in which case pass, because I trust the Spurs front office, or they keep him.
His salary would only be "peanuts" for the first year or two, but could then balloon to max levels after that. Plus, a small market team paying the luxury tax to that extent is highly unlikely, even if they got Durant. Boban is not likely to be back with the Spurs as they have as good a shot at Durant as anyone, and it doesn't mean letting him go "shows what they think of him," it means you let him go 100 out of 100 times for a shot at Durant. And even not taking Durant into account I doubt they want to pay 10 to 15 mil in years 3 and 4 if not more than that. We can just agree to disagree.
It only balloons if someone offers him a ridiculous contract making the Spurs not want to match. I didn't think that's what you were suggesting the Celtics do.
To clarify, his cap hold is $1.44 million. If they renounce his cap hold, they would create $900k cap room, because they would still need a cap hold of the minimum salary of $543k, since they would have under twelve players and holds on their roster (in the scenario where they trade three players to create room for KD). Durant signs, they could go above the cap to sign Boban, and accordingly match reasonable offers. Now, we may have a disagreement about what a reasonable offer is for someone who turns 28 this summer, and had one season of nice advanced stats, albeit in 10 minutes a game mostly against opponents' scrubs. If you think reasonable is 3 years, $24 million total, then yes, the Spurs won't match, and personally I'm not interested. If you think it's 2 years and $6 million total, then they very likely will, unless they have insider information that tells them otherwise. I think they match up to 3 years, $12 million total, and I'm not really a fan of paying more than that.
EDIT: Also, the luxury tax line is about $20 million more than the salary cap, so the Spurs are not in danger of paying it under virtually any scenario.