The easiest way to enter the € Euro Symbol via shortcut is the following:
Go to Settings> Keyboard > Keyboard Shortcuts: View and Customize Shortcuts
Click Customized Shortcuts
Create two shortcuts, one for the Dollar Sign and one for the Euro sign.
Command: xmodmap -e "keycode 13 = 4 dollar 4 dollar"
Shortcut: Ctrl+Alt+D
Command: xmodmap -e "keycode 13 = 4 EuroSign 4 EuroSign"
Shortcut: Ctrl+Alt+E
Now if you want, for example, to change the $ sign
Press Ctrl+Alt+D and then Shift+4
Now if you want, for example, to change the € sign
Press Ctrl+Alt+E and then Shift+4
Enjoy!