Mint LCI halogen headlights will set you back £300. Ones with broken or repaired lugs will be around £250. I got a pair from a breakers with one broken tab for £240 and then fixed it.
Don't forget, you need the front bumper and grilles to go with the bonnet. Actually don't need to swap it to fit fronts, only rears.
MY14 Space Grey F11 530d M-Sport