In plain terms, all cars are expensive to run these days. Although, some more than others.
You can arm yourself with some information by getting yourself some insurance quotes and researching how much it'll cost you at the pumps every 500 miles.
Servicing bills are likely to be higher than the typical hatchbacks on the basis that BMW parts are more expensive. That said, if you do your own servicing you can cut costs a little here.
On the other hand, because it's a BMW it'll likely hold it's value a little better against other options from, say, vauxhall or renault.
Beyond that, why not peruse autotrader and see if you are able to pick something up within budget?
Lastly, I was always taught if you want something badly enough you'll work hard until you get it.