On Excel class ships (Mardi Gras, Celebration, Jubilee), coves are on deck 5, and there is another passenger deck below you. We loved our cove balcony on the Mardi Gras, and I would book it again without a second thought.
Here's the pricing from Carnival's travel agent's site
Carnival's Wi-Fi Service
Package
Pre-Cruise Purchase
Onboard Purchase
OnboardSingle Day Purchase
Social
$8.50 per day
$10.00 per day
N/A
Value
$11.05 per day
$13.00 per day
$17.00 per 24 hours
Premium
$14.45 per day
$17.00 per day
$25.00 per 24 hours
Prices are based on cruise-long plans and are subject to change without prior notice.