Explore the option of having the alternator rebuilt. Look for an auto electrical shop. Typically, alternator rebuild includes checking/replacing the bearings, brushes and/or voltage regulator. Or, look for rebuilt alternator with warranty. You should find one for less than $300.
On a N52 engine, it's relatively easy to remove the alternator; drop the drive belt, remove the air box, remove the 4 bolts holding the alternator, disconnect one-wire-connector on the alternator and remove the nut that's holding the positive cable. Careful, alternator is quite heavy. One of the idler pullies is attached to the alternator assembly. You can replace that idler pulley if it was never replaced.