As stated previously, there are many variables in how much the average (for lack of better term) pilgrim spends per day while walking the Camino (Frances in the case). Just what is an average pilgrim? I have been on this forum for only a short bit of time, but from what I can see, and mind you I'm just guessing, most of the most active members of this forum seem to fall into the same demographics of sorts, and I suppose I am in the same demographic. That demographic appears to be older and less concerned of walking the Camino on a frugal budget, and very likely to spend gobs of money on equipment. I'm not trying to be offensive by saying that, but when one actually walks the Camino, one observes the demographics of pilgrims to be much more diverse than the forum members. A great many I saw (especially younger pilgrims) had very little money to spend daily, and meals for them are often a tin of fish or chicken, some bread and fruit perhaps. They stay in the municipal albergues, and some of those municipals are donativo, and gratis for those that truly cannot afford to stay in them, but I have heard that there are better off pilgrims that stay in them and do not donate. That's bad. I hope none of the forum members have ever done that. I would say to the pilgrims who can afford it, stay in the private albergues if there is a long queue at the municipal. Many of those in the queue can only afford to stay there.
For a pilgrim who has disposable income? 30-40 euros a day.
For a pilgrim on a tight budget? You can do it for 20 euros a day.