i'm pretty sure there's differences in the amout of work put into the instrument- ie how much is done by hand vs machine, and such. also, my beginner clarinet doesnt have all the alternate keys (my clarinet teacher was scandalized when i told him my soprano doesnt have a left hand C/low F key.) then of course there's quality of materials...

someone else can probably answer more thoroughly, but that's a general idea.

im by no means an expert on this area, however, it seems that beginer models are generally made from plastic/resin, low end intermediate are made from composite materials (i.e. wood fibres), and high intermediate and professional are cut from solid wood