Acommodation in Mainz & Pforzheim

Hi
I'm going to Mainz and Pforzheim and I'm having trouble booking youth hostels in those areas as they have no vacancies on the dates I'll be arriving. Does anyone know of any cheap places to stay in either of these areas (preferably central).
Thanks.

The youth hostels in both places would have been also not exactly central.

Mainz accommodation
IB Jugendgästehaus Pforzheim
Pforzheim accommodation

I don't know of cheap places, but you could join a hospitality exchange network like Hospitality Club or CouchSurfing and choose from hundreds of locals in both cities who'll offer to host you for free. In Mainz, for example, HC has over 600 members, many of them living in the city centre.