Habeneros aren't common there, but in general for cheap chilis, try the Turkish grocery stores (EuroGida or similar). Basically for any Mexican / Latin-American stuff, they're great for sourcing ingredients: chilis, dry beans, corn meal, flour tortillas (durum) and will be a lot cheaper than specialty shops. Chilis are also easy to grow (I'm growing 4 kinds on my balcony in Berlin), and one habanero plant goes a long way.