Support packages can vary, but you should always check what is included before you purchase a new system.
Some providers may not charge you up front for support, but they will bill you for every call that is made to the support desk. Other providers may charge you a monthly support fee for standard calls to the help desk, but bill you for what they deem excessive support if the help desk is used too much. You should also look for an all-inclusive support package, where you pay a small amount per month and all support queries (whether they be calls or emails) are included.
Depending on which company you choose to use, you may also be given remote support. This is when a support agent remotely accesses your computer when you call for help. They can see and control your screen, allowing them to witness what problem you are experiencing and manually intervene for you. Again, you need to check whether this is included in your package or whether you will have to pay extra for it.