This cost me $35:

You need a friend.
Stand flat footed with shoes, no cleats.
Have your friend put a small piece of tape at the spot that the bone sticks out behind the big toe.
Repeat on the side behind the small toe.
Repeat on other shoe.
Take off shoes.
Draw a line between the two pieces of tape.
Your cleats should be centered on that line.
Done. Make minor adjustments if necessary from that location.