Based on the kinds of the tools you have, I will provide the cheapest way for you to change your spark plug. There are 3 key pieces:
1. the spark plug socket (rubber socket, magnetic socket or spring socket) , did you know you can make your own socket for changing the spark plug?
2. the gap gauge
3. the wrench extension set.
Since you don’t change your spark plug many times, you may not choose to buy a special tool. I claim to be the cheapest.