In thirtybees / prestashop, there is only one price stored inside database. It's called retail price, or base price:
Final price is calculated from this price. There are many factors that impact final price, such as tax, group discount, cart rules, specific prices, currency, etc.
I understand that you *want* to enter final price, but that just can't be done. Final price is always calculated.
So, if you want to always have the same final price, you need to use Specific prices -- you need to set specific / different base price for every EU country, so the final price will match.
Or you can try to achieve this using cart rules, and apply (possibly negative) discount to customers from different countries.