There are a number of ways to reduce the cost of your geyser from turning down the thermostat, installing a timer and using less hot water. These are low cost solutions with relatively small savings. Larger savings can be achieved if you invest in a solar hot water system or heat pump but these solutions are often prohibitively expensive and can take over 4-5 years to pay off. There are maintenance requirements as well with both systems.
Another way to heat your geyser is to use solar PV panels and the XTEND element which combine well as the XTEND element has a low consistent draw which is perfect for solar PV systems. Turning the geyser on during the day then uses the solar to heat the geyser for free as it provides AC power from the inverter directly to the XTEND element. This is the future of heating your water as the solar continues to provide power to the house after the geyser is warm, unlike other solar hot water systems or heat pumps, and there is virtually no maintenance. Furthermore, XTEND elements last longer than standard resistive elements and perform better over time.