Ok, so if there is only one enemy i think this solution might help you:
You need to tell your Widget where to get the Money-Value from.
This will be your Eater_BP I guess. The easiest way to access your Eater_BP will be to store it in the GameMode. Since you have an interface you can use this as variable type.
So everything that uses your interface can be assigned. This is how the Eater_BP assigns it self to the GameMode when spawned:
And now you have access to your Eater_BP and the Money within the Widget:
Since you have access to the GameMode from everywhere, you can access the Boss-Variable too:
I hope that helps 
Marooney