If we talk about a super expensive purchase that would be good for Real Madrid, then I would choose Haaland. You can watch him until the end of the season (for his susceptibility to injuries - there is a danger that he has an increased one) and if everything is fine, then prepare the transition. Haaland looks like a real professional, I think he would suit Real Madrid in all respects.
Since arriving from Dortmund, Haaland has been one of the most prolific players in the Manchester City squad. It is unlikely that Manchester City will let Haaland go before his goal is achieved. Manchester City has high hopes on Haaland to achieve his goals this season, the Champions League which has never been won will be Manchester City only target this season. Real Madrid must shift their focus to other players because it is very unlikely that they will be able to sign Haaland.