At 103 M€ + Adds cannot be called a bargain, but unlike other Madrid's youngsters, if everything goes moderately well for him, I can see Bellingham leaving after ¿4-5? years to a Premiere League top team, being still very young at 23-24 yo and Madrid cashing profit from the sale.
The gap of the Premiere League with the other European leagues will only get wider in the coming seasons due to the foreign money investments, and even Madrid won't be able to retain a British star player outside of the PL.