FWIW I am budgeting €500 total for my entire CP in April. That does not include transport to Porto or from Santiago or the cost of luggage transfer should I decide that is what I will do. It does include at least two stays in nicer places in Santiago and Barcelos. I figure at least four or five nights in €25 a night places will balance it all out. For food I expect to eat a lot of Frango (€12?) which I hope to get a second meal out of as left overs. I figure Frango for lunch and the rest at supper time and buy yummy stuff at markets (i.e ham, cheese, bread). I plan to carry no more than €150-200 at any one time and the rest will be plastic. ATM are not that hard to find anywhere any more.
I will likely not use cash for stays in accommodations unless only method accepted.
As to safety I suppose I will have to decide how and where to carry it when there but in many previous trips (not Camino) my front pocket in a money clip for the bulk and a second smaller stash in other pocket for taking out to spend in public. Never in my wallet or back pocket. I do accumulate many coins and often times this can be €20-30 in my backpack. All those €2 coins add up and in US we never use our change that way. So it builds up. Weight being an issue I expect to spend coins on daily coffee, snacks and try to prevent accumulation.
I am imaging at least a few very cheap days with dormitory accommodations and small meals. For me, this will be part of the entire experience. Clearly pilgrims come in all shapes, sizes and financial means. I know folks (personally) that spent $2K each on a guided walk and I know of (not personally) folks that spent next to nothing staying outdoors, auberge and religious dorms. You could get by on >€20 a day if you wanted I am sure.