Is $395.96 a good price for this dishwasher?

Yes. That is at the low end of its recent range and well below the mid-$500s it often sells for. Six stores list it new, so compare installation and delivery terms before buying.

How loud is the Samsung DW80CG4021SR?

It is rated 53 dBA, which is average for a budget dishwasher but louder than quiet models rated 44 to 48 dBA. It suits a closed kitchen better than an open living space.

Does it have a third rack?

No. It has two racks with adjustable tines and no dedicated top rack for silverware, so utensils go in the basket.

What cycles and options does it offer?

It has Auto, Heavy, Normal and one more cycle, plus hi-temp wash and NSF-certified sanitize options. Delay start runs 3, 6 or 9 hours.

How much water and energy does it use?

It uses about 3.2 gallons per cycle and 239 kWh per year, and it is Energy Star certified.

Will it fit a standard 24-inch opening?

It is 23.8 inches wide, 24.6 inches deep and 35.1 inches tall, sized for a standard 24-inch cutout. Check depth clearance for the door swing and hoses.