It will not be very difficult for Real Madrid to get Bellingham if they wish to get him. It is not always a problem for Madrid to get any player they want before they have the money and again they cannot be seen as the biggest club in Europe which every player will like to play in for prestige and fame. Bellingham himself will be happy to play on the big stage of Madrid.
Perhaps I am a little out of date on the news, but as far as I know Liverpool have been cited as favorites to sign Bellingham in their desperation to supply reinforcements to the midfield sector. Real Madrid are also targeting this player and would even be the most likely destination for the young Englishman. However, it seems to me that the one with the most real chances of signing him is Chelsea.
I read in The Sun that Chelsea put the player as a priority for the next transfer windows and even knowing the very high cost that will probably involve the negotiation, this doesn't seem to be a problem.
Borussia Dortmund set a value that exceeds 100 million euros to start negotiations for the midfielder, and I think Chelsea are in a position to supply that amount.