I use to organize my parties in this place in P.berg:
http://www.knoblauchrestaurant.de/It is a restaurant but they rent their cellar for parties. It can hold about 45 people sitting and a little bit more if you do not need all the tables and chairs (just enough for you 75). There is a bar. You can bring your own drinks if you want and use their fridge to keep them cool or you can buy drinks from there. They provide glasses. If you are offering food, they provide you the plates, utensils and buffet warmers. They keep washing plates and glasses for you upon request. There is a little stage and a very basic PA is included. A beamer can be provided for a little extra charge (I think 20 euros).
The price is about 160 or 180 euros, you can start your party at any time and you can go until 1 am. Any additional hour after 1 am will cost you 10 euros extra (this money goes to the person who sill stay there waiting for you to finish), my last party went until 5 am.
The cleaning of the place is included in the price, you only have to bring back everything you brought with you. If the cellar is not booked for the next day early, you can even leave your stuff there and pick it up the next day.
If you are interested, give them a call and ask for Mario. I am not related to them at all, but I organized a couple of parties there and I was extremely happy with the service. Mario and his team rule.
PS. you can invite me