Development of a product which is inexpensive, low-power, and wireless is now possible.
Now under development is a capability to deploy wireless solar-powered nodes which communicate with one another, controlled by a base-station. The nodes can send messages containing their sensor readings which are then processed, logged, and displayed by the base-station.. These nodes can run years on a battery, and re-charge their batteries using solar power. The most exciting part is that they can be built relatively cheaply. The goal is to get to a point where they are on the order of $20 each.
By having numerous inexpensive nodes, it also makes it easier to customize the total network to contain the capabilities requested or required for the task at hand. Since the wireless node communications are all inter-operable, adding an additional sensor will be very easy.