I’m buying a used car that needs a wheel bearing on the drivers side? Is that expensive? is it worth it ? It’s a 2006 Mazda mazda3 I 4AT?

Have it checked out first. I doubt it needs a wheel bearing, but if it does, this car might have been involved in an accident If a good mechanic is inspecting it, they'll be able to tell. Good luck.

Yes, cheap do both sides then you dont have to worry  and easy to do yourself

It does not need wheel bearings.  IT MIGHT NEED BRAKE PADS & ROTORS THOUGH. Still not a major cost and you do need brakes. Both front wheels get done at the same time. Maybe $250?

Have you test driven the car yet?  Who told you "it just needs a wheel bearing"? It looks like you are being scammed here if you have not test driven the car.

Parts maybe about $50.  Labor about $100.  I would not buy any car that needs repairs.

Just do it yourself for around $60 - $120. Autozone will lend you the press for free (just leave a deposit) and it takes less than an hour.

Wheel bearings are not major repairs.  Both the part and the labor should be less than $100 each.  But like someone else said, make sure you get the car checked out thoroughly before you decide to buy it.  A car that old, it would be a miracle if that was the worst thing it needed.

Scott is correct, just had one done on my jeep for 4 hundred/plus sensor.

Have a good, independent mechanic check the car fully so that you can learn what else is wrong. Any time I've bought a car with that kind of age and not had it inspected I've shoved in another $3000 to $5000 just to get it into good shape so I could drive it.

Caveat emptor. (This is perhaps the best piece of Latin to know.)

It will cost between 500 and 800 dollars roughly.