Any smart device that you implement in your home is going to come with some type of expense. Many of these devices will justify the investment in tangible money and energy savings while others have features that provide a convenience benefit.
If it is peace of mind you are after, starting small and building over time might work best for you. Begin with a doorbell camera or a thermostat then expand to lighting controls or even a garage door opener later. Smart home automation can be implemented in a rhythm that is most comfortable for you. The decisions are all yours!