1989 Honda Civic Alternator

I have Honda Civic 99 EX with 90K miles. Recently the ABS, Battery and SRS lights were coming on and the radio was cutting out. The garage said the alternator was charging at 19volts not the standard 14volts. The estimate for parts & labor is $510. 1) Is this a good diagnosis, 2) Is this a resonable price? He said they only use quality parts they can warranty and this is a great part specifcally for Asian cars. Said the cheaper ones you can find on-line are ususally garbage. As a side note - this garage has always been very nice and in the past perfomed minor tests for free. However, this price seems a little high. Thanks