Please book a hotel on your own. Here is a short list of Hotels near Mainz main station or University:
Near Main Station
Hotel Königshof, Schottstr. 1-5 , 55116 Mainz (special University rate available: 68€/single room, 75€/ double room used by single person, both incl. breakfast)
City-Hotel Neubrunnenhof, Große Bleiche 26, 55116 Mainz
Advena Europa Hotel, Kaiserstr. 7, 55116 Mainz
InterCity Hotel, Binger Str. 21, 55131 Mainz
Hotel Hammer, Bahnhofplatz 6, 55116 Mainz
Near University/HIM:
Hotel Römerstein, Draiser Str. 136 f, 55128 Mainz (small house in walking distance to University/HIM; special University rate 70,50 €/single, 93 € double room both incl. breakfast)
ParkInn by Radisson, Haifa-Allee 8, 55128 Mainz, (no walking distance but easy to reach by car within 5 min.)