Tomaz, what i do, is i fly to Holland, and drive with my dutch gang to Wacken (about 6 hours drive)
you can find great deals for Holland. i'd say around 600-700$ sometimes even less, it all depends on how good your travel agent is...
the whole trip to wacken including flights, hotels for the first days (i assume you will camp there if you'll go....) food, drinks and some shopping shouldnt cost more than 2000 - 2500$
of course- if you plan to go only to the festival without buying anything- it shouldnt be more than 1800-1900$.
hope i answered your question