There are many accommodation options in Düsseldorf, many of which are quite affordable (unless there’s a trade fair in the city, which doesn’t seem to be the case during our conference).
We have blocked 50 rooms in a hotel conveniently located near the University (HK Hotel Düsseldorf City) for conference participants. If you want to book one of the rooms, you can do so by contacting the hotel via email or phone and mentioning the super-secret and totally non-obvious keyword “Protolang”. Single rooms are 80€/night, double rooms 100€/night (incl. breakfast). Free cancellation is possible until 7 days before arrival.