Sorry to hear of your troubles, it sounds like you picked up a car that was really never well taken care of and a dealer who just wants you to go away. You're probably sick of the sight of the thing. That warranty sounds very expensive and could have bought a whole lot of preventative maintenance right after purchase instead. There is no timing belt in our cars so of course they told you an expensive item like that is covered. I think the lesson to be learned here is to get a Pre Purchase Inspection (PPI) before any used car purchase, especially an expensive mark like a BMW.
No Lemon Law on used cars, BTW.
I wish I could offer something more constructive, either sell it (at a loss) or keep dumping money into it until the problems are fixed. Either way will be more money out of your pocket. You could make a case with the dealer that sold it to you but that will end up taking more time (and money, possibly). Expensive life lesson - sorry man...