Went to the SPARC office to get my bike and take it to the cardboard-box-shop to get a box of the right size. The boss had one of the guys working at the office, Sunam, accompany me to do the negotiations. The biggest box they had at the shop was too small and they still wanted to charge 10 Euros for it.
Sunam knew another scrap dealer and I got a fridge box for a more reasonable price there. I modified the box for the bike to fit properly and packed everything up.