There are 2 options: interconnected and non-interconnected.
Non-interconnected systems are much easier to install, but lack the total security management that interconnected systems have. There are also additional maintenance issues. Hotels commonly use non-interconnected systems. Each lock contains a reader, battery, electronic module, real-time clock and/or other authorisation device.
Cards can be programmed for 1 or more locks, with explicit start and expiry times. So, if you book into a hotel for a week, they will program your card for your room, for one week. If the card is lost, it can't be disabled.
If the lock battery runs out, or its clock drifts, then the lock may not accept an authorized card.
Locks may or may not record activity. If they do, then it is a manual task to read the data out of the lock.
Interconnected systems connect a card reader (either magnetic stripe or RFID) to a central computer, which then controls the locks on individual doors. There is a significant infrastructure cost in installing all the cabling.
The system has the advantage that all accesses can be logged and monitored remotely, and that any card can be deactivated immediately. The system should also be lower maintenance, as there are no batteries to replace regularly.
All said, I think in your circumstances, a hotel-type system would be the best bet. You will probably only need a few locks (so the high cost of the individual locks shouldn't be too bad), and the need to replace 6 batteries annually shouldn't be a problem - it's not like this is a big hospital with 5000 doors. You should contact a locksmith that specialises in this type of system - they will be able to explain exactly what is needed for the whole system. Usually, you just buy the locks, and a programmer which connects to a PC with some management software.