A brand-new cheap student/sports hotel with 120 bed (1, 2 or 4 bed rooms): https://www.wiro.de/wirotel-mittelmole/wir-ueber-uns.html It is next to the camping area.
Notes on booking: A sports group in the WIROtel Mittelmole consists of at least 4 persons. To book as a sports group, please present a confirmation of participation or an invitation to a sports event in Rostock. (In your case use either your registration to the Worlds or at least the NoR.)
For more information and an individual offer please use the inquiry form on this page or contact the hotel directly.