might be a bit over your budget... not 100% sure of the euro to dollar conversion or your prices over there. in general just look for a really closed off case, you probably wont find many cheap cases built for silence. keep in mind all your components contribute to noise level, a quite case isnt a magic bullet for noise. ( at best you muffle the sound )
quiet components in an open case would be better than noisy ones in a quiet case.( you will also sacrifice some temperature efficiency in quiet cases)