As long as you maintain good progress (GPA >3, research, TA/RA duties, etc), you will get the funding, and won't have to fight for it. Most students who get admitted are given funding for 4 or 5 years or till they graduate on a condition that they maintain satisfactory performance. Don't worry, you will not have money problems.
if you want to quit later, why accept now? doesn't make sense to me. but once you sign the letter, you are legally bound, i think. it's up to the school then to release you or do whatever.
just found this housing website, and though i should share with you all who are heading to U of M coming fall: http://uofmrentals.com/
disclaimer: i do not own or work for this site. this is strictly for prospective Minnesota students.
i think most biology MS students get funding. all my friends (all MS) at my school and those who joined other programs got good funding for full 2 years. i do not know what goes on in other programs, but contacting few professors to see if they RA position available is a good idea. but as hamster said, don't rely on your professor. email the current grad students and find out how they've been managing. i am sure you aren't the first MA student to join this department, so others, who are already there, should be able to provide you with some pointers.
good luck!