When someone you love is going to benefit from a service like this, price shouldn't even enter into the picture. You get what you pay for. The monitoring station that's going to be responding to your signals should be UL (or ULC in Canada) and/or FM listed. This ensures the physical station and the personell have met an acceptable standard when it comes to the equipment they employ, the protection level of the monitoring station, and the type of training the staff receive that will be dealing with your call for help. I personally recommend a "local" station (that is "local" to your relative's home), but a number of the "nationals" also provide excellent services using toll free - out-of=state monitoring. Make sure the station you contemplate using meets all the criteria set by your local municipal codes and bylaws. It's often a good idea to contact the local licensing authority to confirm that the firm you're using actually *employs* licensed and screened staff.
What's the panel testing schedule? Daily? Weekly? what's the local authorities response to a false alarm (fines, penalties)? What area of the country do you live in?? Make darn sure that if you are contemplating a "national service", that they offer response *in your area*.