If you have a machine shop near you, or better, own a press, you can have the bearing pressed out the original pulley and have a new bearing pressed in. The part number is 6203-2RS for Wagner or/and others I believe. You can find them online for as little as $3, and it'll be good as new.
I have replaced both of my pulleys over the years, the top pulley is available, as the bearing cannot be easily changed out the original style. The lower A/C pulley is not available anywhere I found, and I searched many resources, but the bearing can be pressed out and new one pressed in with the part number listed above.
If a bearing is making noise, it WILL eventually fail. I learned the hard way with my top pulley. I was sitting in traffic one day, and turned on the A/C, the pulley started whining a lot, then I heard the whining stop, and saw smoke coming out from under the hood, with the smell or burnt rubber. Shortly after the battery light came on, and I pulled over and found the top pulley froze up solid, and shredded the belt to pieces. Thankfully the drive home wasn't far, so I limped it home without the A/C and alternator, and changed the pulley, and put on a new belt.
Hope this helps.