Cost to replace front wheel bearing?

loose bolts somewhere in the front end? you have had lots of work done there. wheel weights can fall off or a rim can be difficult to balance?

If its not the bearing and your Mercury is front wheel drive, it could be the "CV" joints.
It could be both....

Is the wheel rubbing the brake caliper?

Is something like the wheel well liner rubbing the tire(airflow pushing it into tire)?

Jack the tire off the ground and rotate it by hand. Push in & out at the top, sides, and bottom of the tire. Little or no play is considered acceptable. If you get a "clunking" sound and/or a lot of play the bearing(s) are bad. (If front wheel drive, chock rear tires, put transmission in neutral so you can rotate tire.)

Hope this helps.

Wheel bearings are sealed on this particular GM vehicle. First thing to try is to place the front tires on the back of the vehicle and see if the sound changes. If the sound still comes from the front, have the wheel bearing checked at your local service center. Expect to pay between $200-250 to replace. If you decide to do it yourself, you can find the part for $60 at places like RockAuto.com.

Wheel bearings will generally last around 200K miles before they begin to show signs of failure. If you hit a curb on that side recently, that could cause a premature failure.

Since you drive a 300, About $250.00 per side.

The hub bearing is some thing that goes into the spindle so that the wheel can turn freely, it is also a seal bearing unit, to remove and replace the wheel hub bearing you will need a press to press out and press in the new hub bearing into the spindle.

on that vehicle it,s replacement remove wheel remove brake caliper and pads remove brake caliper mount if you look on back side of spindle around area where axle comes thru you have three or four bolts remove bolts remove axle nut and hub bearing assembly comes off re-install in reverse order if this vehicle has 4 wheel abs unhook any wheel speed sensors

raise the car on that side grab the tire and see if has any( play) moves from side to side considerably.

The noise you're hearing is consistent with a bad wheel bearing. It's true, the only way to actually tell is to pull the hub/bearing. I'd try to isolate what side of the car the noise is coming from and pull that wheel. If it's not a wheel bearing, it could be transmission related but these things are usually solved by replacing the wheel bearing.

Assuming both shop quotes are for BOTH front wheel bearings AND LABOR....
the first quote is ok...the second sounds fishy...(or the quote is just for one side)
Also a factor is the parts.....new,, used or refurbished....

In my humble opinion, I would say this is not normal wear and tear. If it were me I would get a 2nd opinion. I have been driving for over 40 years and I do not remember the last time I had to replace a wheel bearing. I'm not saying it can't happen but another opinion would be worth the nominal cost.

And if the answer is a strong "it's not needed" I would find another mechanic than the one that gave you the estimate

Hope this helps Loringh