That's actually only cheap because of the free shipping - in Germany 450W panels are at about 55-60€ retail right now, for example. So a balcony set (2 panels for 1kW total, plus inverter) is about 150-200€, depending on the specific parts. Both exluding shipping, though.

Prices fell dramatically in the last few years, if I understood things correctly the high prices in the US are mostly due to tariffs.