"When you're talking about time, up to is followed by a general term that covers a span of time. Until is followed by a specific point in time.

Examples:
I can wait up to three days for your answer (but I can't wait any longer).
I can wait until 5:00 for your answer (but I can't wait any longer)."

http://forum.wordreference.com/showthread.php...

In your examples I would say:
I went to school up to the 12th grade.
I was at the party till the end.
The television costs up to 1000 euros.

First of all, thanks to both of you!! :)

But I don't get why hermarphromoose is using "up to" in the first example.
I mean the 12th grade is a specific point in time, isnt it?

I admit, with the first one the first thing that came to mind was "till" the 12th grade, and then after I thought about it a bit, decided that "up to" fit better. But I think this is one example that could really go either way, depending on how you view the time unit "12th grade".
If you think of it as a unit lasting a whole year long, then "up to" is right. If you think of it more as like a single step in a sequence (1st grade being the 1st step, then 2nd grade, 3rd, and so on all the way up to 12), then I think "till" works too.

(Now I am making myself unsure, though, after seeing how I used "up to 12" in my last sentence. *sigh*)