You can buy a new water heater heating element and thermostat kit for around $35.00 to $50.00 then to get the tool to remove the water heating element is around $5.00 to $10.00
So you can replace the water heating elements for around $40.00 to $60.00 in parts and a little know how.
But if you're unsure about how to replace the heating elements or how to work with electricity then you can hire a handyman to do the job for a lot less than a plumber would charge to replace the heating elements.
A licensed plumber may charge around $200.00 to $250.00 including the service charge and parts and labor to replace the heating element while a handyman may be able to replace the water heater heating elements for around $50.00 to $100.00 in labor costs.
Plus the cost of the parts.