Why not get on the web and get some quotes for yourself.?
Try autoeurope or other similar vendors. etc.
There are at least a half dozen well known rental agencies that you could access to view specific rental rates. Hertz, Europcar, Avis, Budget, Sixt etc.
We found the prices varied very much from country to country, vendor to vendor. Airport rentals are often more expensive than city rentals. Portugal was far more expensive than Greece. Most of our rentals are one way. We buy the smallest car for the two of us and we have no issue whatsoever with a standard transmission. In some countries we prefer it.
If there are four adults traveling you need to understand how much luggage you will be taking vs the luggage capacity of the car that you hire. We have seen a few instances at rental agencies in Europe where that was an obvious mismatch between luggage and trunk space.
It also depends on when you rent, how long you rent for, and to a certain extent where you rent. This is a demand and supply business.
We find it less expensive to arrange a rental before we go. Rental prices change. If you reserve, keep shopping the prices. We have realized reductions on several autoeurope bookings because of downward price changes.
You might also want to understand what car rental insurance you might have from your credit card provider and/or from your auto insurance provider