I don't think this is a good approach, especially for those planning to walk shorter distances each day. The reason is that the major cost drivers are accommodation and meals, both daily costs, NOT distance related costs.
If you do want to take the risk of this approach, I suggest you use 1.5€ / km to give a more realistic estimate that includes some contingency.
Regards
Point taken Dougfitz and you are right.
It certainly depends on many things such as daily km, albergues or hostals, dining out or preparing food with others, and much more.
When I walked Frances I did it in a month and for me it worked out to be a little less than 1000 € on the camino.
Maybe the 'calculator' can be useful for people planning a part of the camino, like SJPP to Burgos; 390 km, ≈12 stages: cost 400+ € for a 'basic' walk. ( even better - go with 1.5 € = 600 €)
I think I will leave it at this and get our before I create more confusion than clarity
Regards
Lettinggo