is it a good idea to pay 760 a month for a 2011 m3 with 91k miles?

Can you set aside another $100 or so for maintenance?

yes I can

why?

true, true, I am actually not going to refinance it, it won't be worth it, it is mainly a car that will sit for awhile till it is fully payed off which is about 28k left?, use it minimal, I am taking over the payment from a friend who has taken extra good care of it and has after market mods, he will be paying for everything before transferring it to me.

paying everything as in paying to fix it, clean, any service needed, etc.

Miles are high for a 2011 but with complete maintenance records $25-$28K is not unreasonable. M3's are expensive to maintain and you should be aware of some of the trouble areas. Throttle Actuators (2) have some inherent design flaws and can be expensive to replace, +/- $1,200 each. Oil changes, at the dealer, will run you around $225. Fluid replacement and general maintenance items are 2-3 times more than most cars. M3's from 2008 to 2013 have the S65 high performance V8 which was pretty much developed for racing. There are a few sites like Bimmerpost that you should go to. Read some of the threads and you'll get some insight into what its like to own a M3. Regardless, a well maintained M3 will easily go 200K miles. Good luck and choose wisely.