Brake Booster & Timing Belt Replacement

How do you know you need to replace the booster? Well, first off, there were at least 2 occassions when I tried braking and the car still moved ahead. I had to pull the handbrake to bring the car to a full stop..thankfully it happened at slow speed and not the highway...
The booster is the big round thing in the box, the chain/belt lookalike is the timing belt. Timing belt needs to be changed very 40,000km if not according to the manual, it will snap, and you dont want that to happen. So what's the damaged...pretty steep...as always, I service my e36 at M&Q Auto Work located at Tampines Safra, block 9004, look for Mr Chia the owner. So how much was the damaged...
1. Brake Booster Assembly - $250
2. Labour - $54
3. Oil service safety check with replacement of timing belt - $160
4. Mobile One - $94
5. Timing Belt Components - $76
6. Oil Filter - $9.60
7. Exhause O Ring - $11
8. Brake Fluid - $4.80