They have the money to do it without selling Alexis, I'm just saying I'd be shocked if they spent that much money on a single player. Replacing Alexis with Thomas Lemar would definitely be hilarious though.
Also yes, Alexis walks free next summer, which is part of the issue. They either sell him right now and get money, or try to convince him to at least put effort into this season and let him to wherever he wants for free next summer.
I can see why they are taking the stance they are taking tbh. They don't want to be a club that sells their best players anymore. It's been additionally embarrassing because they have regularly sold their best players to rival clubs in the same league. This one is probably the main focus, stopping the sale of good players to domestic rivals would be a positive step forward for Arsenal.
You obviously don't want to be known as a club who will keep their players even when they don't want to be there, but the problem has been, once again, the culture at Arsenal. For example, if a top player wants to leave Chelsea they already know they will have to leave the league. Players know Arsenal will sell to whoever, it's part of their current culture. The whole Alexis ordeal is seemingly an attempt to change that.