With the money that Bavaria received from the sale of Lewandowski, it is impossible to buy anyone at all who would correspond to the level of Bavaria. But Bavaria has no shortage of money and can afford much more expensive purchases and I hope they accept this reality that the "cheap" options have run out. I think that Füllkrug is just a cheap option that doesn't fix anything. If you make a purchase, then it must have some meaning.
Bayern Munich is very careful in spending their money, they will not spend money on players of standard quality.
Bayern Munich is not a club that is in financial trouble, the sale of Lewandowski is not much with the cash they currently have. If they bring in players for short-term targets as a coating option for injured key players, they will choose free transfer players. Reportedly Bayern Munich are starting to be interested in signing Ronaldo after his status as a free transfer player, Bayern Munich does not need to spend money to sign Ronaldo as an option to replace the injured Mane.
I don't know where you heard this because just a few days ago Olive Kahn, on behalf of Bayern, ruled out signing Ronaldo.
Free players are no longer free - this is the new reality. Look at the size of Mbappe's or Haaland's signing bonuses - previously such amounts would have been record amounts for a regular transfer, but now it's just a signing bonus.
I think if Bayern Munich is targeting this season's Champions League title, they will be interested in signing Ronaldo. However, it will cost them a lot of money. But Bayern Munich is a very rich club. They need to win titles more than money. And so I will not be surprised if Ronaldo is included in the team. But Bayern Munich will benefit even more if they can sign Mbappe. But we are not sure if Mbappe will leave PSG now.