1997 Subaru Forester Noisy Wheel Bearing

Hello,

I recently purchased a second hand car, which underwent a pre-purchase inspection. This inspection revealed no faults of the car, except it needed a wheel alignment. I took the car to have this done, and in the days leading up to this, I noticed a whirring noise coming from the front left side. The mechanic who undertook the wheel alignment also noticed it, and indicated taht it was a noisy wheel bearing. Something about the hub, and that it could be wearing it down through use. He said it could be anywhere from $200-400 or more if its bad, to fix. He doesnt know which wheel it is (although it sounds to me like front left), and wont know how bad it is until he gets inside.

Just wondering if that price sounds reasonable, and if it sounds like he could easily rip me off. Also, should the pre purchase inpsection mechanic have noticed this? It seems to me like he should have.

Thanks you.

Sam.