Cannot determine any 'fair' price until you have obtained written quotes from 2-3 trusted repair shops in your area, comparing the same work (parts and labor).
The quoted price you have is far too expensive ($750.00!) for simply changing the alternator. Save the excess labor - buy a repair manual, or reference one at your local library and keep the labor cost $$ in your pocket!
One question - does the quoted price for the alternator replacement include the replacement serpentine drive belt, and belt idler pulley as a kit? The quoted price is still too high - even if the other required parts are included.
For safety and reliability sake - it is recommended to always replace the serpentine drive belt and the idler pulley at the same time as installing a new or rebuilt/remanufactured alternator.
Try these on-line parts vendors: www.autopartsanything.com, www.partsgeek.com, www.rockauto.com - to list a few.
In fact, they (RockAuto) list the alternator from around $77.00 (remanufactured) or new from around $90.00
remanufactured = MAGNETI MARELLI part # RMMAL00118 - or it's equivalent
new = WAI GLOBAL part # 13787N - or it's equivalent
The serpentine drive belt(alternator) is around $3.00 ~$5.00
ROADMAX part #4K305AP - or it's equivalent
CONTINENTAL part #305K4 - or it's equivalent
The drive belt idler pulley is around $32.00
DAYCO part #89523 - or'it's equivalent
Total parts cost = $105.00 - $120.00 and of course this does not include the labor to remove / replace parts.
Recommend for you to: obtain more written quotes - watch some videos, and read the repair manual - and keep the extra $600.00 or so in your wallet!