400W solar panels cost $200-250. So 2400W will cost me roughly $1800. There are discounts if you can buy in bulk, but I don't have room for more than 6-8 panels at most.
Like all things, the raw material cost is trivial. There are the tariffs you mention (I just skimmed your link, and don't speak German), but there's also economy of scale, packaging, logistics, etc. I'm sure I could get 400W panels for as little as $100/ea if I went to the factory myself and bought hundreds of them. Maybe even cheaper. It's not really fair to compare consumer one-off costs to industrial/commercial-scale installation costs.