SMS's cost 0,48 DKK for danish customers (1 unit is 160 characters)
SMS's are reloaded with 1000 units at a time, when you have used your 1000 units, and are then added to your bill for next month's subscription.
That means if you have used up all your SMS's, then you will be billed for 480 DKK on the next invoice and you then have 1000 units you can use, before it gets reloaded.
You can always see how many SMS you have left under Settings -> Subscription.
There are no SMS's included in the subscription packages themselves.
The price for SMS is determined based on the costs of sending through the providers and is fixed (no discounts).
This is the same for most other countries.