Vehicle Steering wobbles during light braking

I'd pick a different mechanic to start with - wheel bearings could normally be diagnosed if they were the issue. From what you've said so far, chances of them being bad are very low and there's no reason to have them replaced this early in this process. Before replacing the steering rack, I'd have the tie rods checked first, they are a lot cheaper to replace than the steering rack. I'd also recommend inspecting the calipers for uneven movement as that could cause vibration during light braking even with new rotors.

Once you have had the wheels balanced, and eliminated warped rotors, any remaining wobbles in the front end can usually be attributed to bushings, and there are a fair number of them:

• Tie Rod bushings, Balljoints, these are the ends of the steering rack that attach to the wheel spindle/knuckle.
• Steering Rack Bushings (holding the steering rack to the body)
• Engine Mounts
• Control Arm bushings, these hold the steering knuckles in place and connect the knuckle to the body of the car.
• Suspension bushings such as the strut top mounts

Most bushings are rubber and you can inspect them for worn and brittle rubber that is visible and possibly crumbling. Some bushings are brass and as such these are usually much harder to inspect. The most basic test is to jack up the car and hold the front wheels with hands at 3 & 9 o'clock and rock back and forth to check for noise & movement, and then hold at 12 and 6 o'clock and do the same rocking to test for noise & movement.