Well, in my experience those things don’t always go together. For instance, Italy is your best bet for history/sightseeing, good on cafes/cost, worse on beer/wine and friendly people. France excellent for sightseeing/cafes/wine, less good on beer/people/cost. Germany great for beer/wine, good on people/sightseeing, crap on food/cost/cafes (though beer-halls are nice). Etc. Of course these are broad generalizations. You might get some suggestions for Czech Republic, which is relatively cheap, has good beer/people, is a lot of fun, but less good on history/sightseeing. It’s a bit far from Barcelona though. There’s also northern Europe, but the costs rise exponentially. Personally, I’d go with Italy as it might be the best overall given your criteria. Maybe Rome/Riveria to split it up. If cost is the most important thing, maybe go CR (Prague/Krumlov?).

I agree Italy is a great choice to meet the majority of the things you’d like to experience. It will be quite warm in Italy in August, so that is something to consider too. Another possibility is Southern France and then take the train to Paris (or vice versa).

Some places in Germany aren’t too hard on the budget.  If you get out of the really big cities, prices tend to be a lot better.  The Mosel River has lots of scenery and history.  There’s the Roman city of Trier (ruins, baths, etc.), well-preserved old-world buildings in Bernkastel, Burg Eltz ( www.burg-eltz.de ) and other castles you can tour, lots of sidewalk cafes (Cochem, Trier) and several hostels (Cochem, Trier, Bernkastel, Traben-Trarbach) or private B&B’s (many at about 20 Euros/night p.p.) 

A few impressions of these places: www.mosel-reisefuehr…

Stay in Cochem (very scenic and atmospheric and well-connected by train) or Trier (larger, good for daytrip to Luxembourg City) and daytrip to the other towns in the area.  Both cities have nice pedestrians-only zones and outdoor cafes.  Cochem has lots of food options including some gourmet offerings:

www.cochem-tourist.d…

If you enjoy biking and hiking, there are well-established paths – really nice biking along the river paths from town to town.  Also lots and lots of wineries in the area – this cellar is in Cochem proper: www.hieronimi-wein.d… .   River boats head out from Cochem to other towns along the windy river (like Beilstein.)

Larger cities (Koblenz, Cologne, Mainz) are nearby.  With a week, you could stay maybe 4 days in this area and 3 days in Bruges, Belgium, or in Amsterdam, which aren’t terribly far away.  They’re a little more expensive but have the sorts of things you are looking for.

Minimum budget means “go east” to me.  Try Croatia, Slovenia, elsewhere in “former Yugoslavia” or maybe Turkey.

Absolutely agree with “Oldlady” – go east!

The Frmr. Yugoslavia is a great place to start, but keep in mind that Croatia’s coast can be more expensive than you think depending on the time of year that you are there.

Bosnia is cheap. Serbia is cheaper. Montenegro is in the middle pricewise.

You might also check out Turkey like OL says – VERY cheap the min. you get out of IST, and even IST isn’t that bad pricewise for a major world city.

Frozenthrone, I’m not sure I understand your post.  If you don’t know where to go, why will you be in Barcelona?  Is that where you will be doing your master’s&nbsprogram?  And you’ll have friends visit you for a week?

Barcelona and Spain themselves have lots to see and do. 

Also, since cost has come up, Italy is not exactly cheap.  It’s quite expensive.  But as Russ pointed out, there’s lots you can do with a low budget, even in the more expensive countries.

Italy is too far.  Rome is too crowded.  Nice Cappucino, though.
 
I would try Paris-Amsterdam-Bruge circuit for a week.  In Paris it is always easy to get away from the crowds and there are tons of outdoor cafes and lots to see. In Rome it is not.  Amsterdam is outdoor cafe heaven.  Stay away from the Centre.  Bruge is charming.  Freindly people = Americans.
 
Good luck.