To get your student visa usually you either have to show that you have 6,000 Euros on your account or you have to have someone sign a form, legally obligating them to support you during your stay in Germany. I don't know how the Auslaenderbehoerde is in Tuebingen, but in Thueringen and Sachsen they are sticklers for having the money on your account. I would also take a look at rent in Tuebingen and figure out how much it will cost. If you don't plan to go out much, don't travel and don't eat in restaurants, you can live comfortably in the depressed areas in the East for about 600 per month including rent, which is about 200 per month. But in the West it is probably more expensive. I would plan for about 700, and maybe 800 per month if you plan to go out a lot or travel at all.
Are you going on a scholarship? Or are you paying your own way?
If you have some sort of DAAD scholarship that covers room, board and tuition (however tiny amount that will be), you'll still want to bring some money. Probably equivalent of at least 200 Euro per month, and really the more the better. You might also be able to get a job, but that is a bit a random.
I've never had to show how much money I had in a bank account when studying or research in Germany, but I've always been affiliated with some sort of program or university.
If you are paying your own way, I have no clue. Proabably at least 700 Euro per month given that you have to pay rent, buy groceries, etc. I'm not sure how AOK (insurance for most uni students under the age of 32 or so) deals with Auslaender who are not coming over on scholarships.
My university provides "exchange tuition". According to my school, my tuition exchanges (it's about three hundred more to go to Germany) and $4,451 goes towards tuition, $2,554 goes to Rooming, $2,189 goes to Board, $1,600 is personal expenses, $1,000 is personal traveil, $850 is airfair, and $322 is insurance.... with study abroad fees, and tuition fees, that comes up to $13,466 that I'm guaranteed..... I guess I should have made my post more clear.
I was in Bonn 3 years ago, the program I went on deposited roughly 140 euros into my account every month and I was fine. I had cooking facilities in my wohnheim but I'm pretty sure I lived off bittburger and doenner the whole time anyway. I didn't go any place outside of germany and i didn't go to october fest or fasching. I did hang out in koeln for karnival and the 7 days of drunkenness, visited aachen, dresden, trier all on my own. I became a fashion victim tho and that alone sent me home with a 1k debt in my pocket. Frankly i think if you are young and you can get a loan you should do it, better than putting everything on credit cards , and then travel all you can because when are you ever going to have the chance again? you can have some amazing times in germany and outside of it, even if you don't drink, go on all the wacky alkohol related tours you can find, they are a lot of fun and the locals will drag you into their groups. Two airlines to keep in mind, billigeflieger.de and ryan air, and do your best to read the tour books about other countries because it's super sad and sucky to get ripped off or scammed when you could have avoided it. My last bit of advice, join an intramural sports team of some kind, I played rugby in Bonn and not only was i really bad at it and never had to play in any real games i got lots of good free german food and free trips all over western germany with the team. oh and i went to a lot of hockey games, that was also an unexpected delight, way fun, lots of german pride, very cool.
have a really great time !