If you ask really nicely I reckon we'd part with Kepa for that amount
Most clubs would sell their goalkeeper for that price, the exception being very wealthy clubs with a genuine world class one.
For 40m-50m I wouldn't be surprised if Lunin is available, the other one that come to mind is Bulka he plays for Nice but was at Chelsea's academy. Even someone like Kovar could return to United for that kind of price.