BMW, compared to your Altima, is going to cost an arm and a leg and maybe a couple trips to the sperm bank, to pay for regular maintenance. It is redonkulous, but at least you'll probably get a free car wash.
When you own a BMW, it is cheaper to do the labor yourself on easy maintenance tasks. The parts cost a lot compared to domestic cars too. I had an older 3-series. The cost of a cap and rotor on a BMW was multiple times higher than an American car distributor cap and rotor. If you would like a 5-series, it's a nice ride, but there's maintenance involved to keep it running well. If you don't do regular maintenance, you are going to get stuck on the side of the road unexpectedly.