If you already have the part, they shouldn't charge any more than $25 or $30. It only takes about 20 minutes labor. If you don't have the part, make sure you ask for a rebuilt alternator. A brand new one will cost three times as much. A rebuilt one will last just as long as a brand new one.How much do they charge to change the alternator?
Go to repairpal.com and look it up. You can find out what a dealership or independent garage would charge in your area code, and it's free.