I'll post my experience since Jan 2014 when I purchased a 211k and Tailgater combo at the tent in Quartsite.
The service is prepaid monthly. You can stop and start your service at your convenience and only the days you use are deducted from your balance.
If you 'cancel' your service before your month is up, you will have a credit balance at Dish. We usually say "we are traveling in an RV and are currently in a location where we don't need the service".
When we next want the service, we call to 'activate'. At this time our credit balance is applied to the cost for another full month. E.g., if we want the $75 plan and have a $25 credit, we pay $50.
HTH;
John