since the last wm berlin has increased their prices everywhere but i still think, overall, it is cheaper than dublin if you know where to eat out, drink and stay
if you stick to tourist places, you will see almost no difference to dublin
what area is the best to stay in the city centre
don't compare berlin to dublin, city centre is almost everywhere - depends what you're looking for and from what angle you look at. zoologischer garten, potsdamer platz, alexanderplatz, hauptbahnhof....they're all considered "city centre" and are not placed right beside each other. berlin has an excellent transport system so wherever you stay - you will have no problems getting around, do sightseeing, go out for drinks etc.
berlin has lots of own brewed beer, so you guys are going to have fun over there and the average price of a beer is around 2 - 3 €
also if you're eating out - i can recommend friedrichshain over mitte for example because it's much cheaper.
enjoy your time over there!