Nice thought but I can't see the board sanctioning a knock down price on that behalf.
If he doesn't fancy him or wants to play a way that doesn't suit Benteke, then his value is going to go down over the season. Palace might be struggling to do much business with limited budget, he is the most saleable asset. Plenty of managers have made a success of selling the main asset and reinvesting, while plenty of clubs have struggled when they've not been able to invest to acquire targets.
At some point, do you think we are missing out on all the players we want because we can't afford them. Maybe De Boer has a few players he thinks are really good and will improve team and are great value, and one or two of those are forwards. If they can get about 50% profit and reinvest in a number of areas, I think board could see value and merit. After all, they've only just hired De Boer and if your not going to back him out the box, then what's the point.
If they wanted to keep him, then there is no discussion to be had as he has just signed for them. That Palace haven't come out and said a big loud piss off, says they don't seem offended about discussing it. It also would tend to imply that they may have alerted our interest in one way or another, if people don't know he's for sale, they won't bid.