I think it does vary depending on where you are on this route. Early on the first few days from SJPDP it is a bit more and if you include meals with your bed, it can run 30-35 Euros not including your lunches or coffee while walking. Later on the meseta in smaller towns and in Galicia at the Xunta albergues beds are a little less, but plan on 10-15 Euros average. Cities are a bit more expensive.
I would say if you have an average budget of 35 Euros a day that is enough for a bed and to feed yourself. Increase your budget to 40-50 Euros per day if you are shipping your bag or need to get occasional transportation. Don't forget items you may not think about like purchases at the pharmacy for blister stuff or aches and pains which can add up.
Build in some cushion in case you get sick and need to hole up somewhere in a private room for a few days. That happened to several people this last year on the forum.