None of us can accurately predict your trip cost, because so depends on choices you make re hotel and food.
Rick's opinion, published in Europe Through the Back Door 2009, is that his readership's average trip cost is about $185 per day per person, including everything except airfare.
The $185/day/person is an average: about 1/2 would be expected to have $185 or somewhat lower and 1/2 a somewhat higher cost.
The RS/ETBD $185 per person per day includes these assumptions:
a couple sharing a $150/night hotel room (thus $75/person)
breakfast included with the hotel rate
lunch $15/person
dinner $25/person
$5 misc snacks/person
The $185/person/day does not include airfare and assumes a couple staying in middle of the road hotels, eating one sit down meal per day, and traveling generally middle of the road.
Some forum members are, understandably, proud of the fact that they do trips for less than Rick's guidelines (we don't seem to hear much from those admitting they spend more than Rick's $185/day). But you may want to be cautious about making the assumption that because others, who travel in a particular way and carefully control costs, can do it for less, you can too--of course it can be done for less (see below, Rick addresses that)--but in travel it's probably true that you don't consistently get what you don't pay for.
Doing it for less means budget choices have to be made. Rick's book gives an alternative budget, for what he calls "student or rock bottom budget travelers," of about $100 to $110/person/day cost, again this includes everything except airfare. This is based on a single traveler staying in a hostel or equivalent dorm type of sleeping accommodations and being very careful about the food budget and not eating regularly in sit down restaurants. The $110-$110 figure is not an average.