A good string trimmer like Ego makes can run you close to $400.00, therein lies the rub. Even a 40 volt Ryobi can run a couple hundred with spare batteries running up to $400.00 depending on Amp capacity. Ryobi's riding zero turn mower has 6 motors and runs over 4 thousand for a 42 inch model. Batteries are the major cost.
My Stihl battery operated hedge trimmer was $199. The battery and charger was another $100.
The battery fits all the other tools in the Stihl series. The only thing I have done to maintain it since purchase is lubricate the blades.
I have 8 small gasoline (4 cycle & 2 cycle) engines pieces of power equipment and a diesel 36HP tractor. I may never buy another 2 cycle piece of equipment again.