During late 2015 from SJPdP to Santiago and then to Finisterre, Muxia and back to Santiato - altogether 36 days of walking I spent 1277€.
I used google sheets on my phone to keep track of _every_ expenditure - from ticket for a bus in Bilbao to daily spending during Camino, from water/chocolate at the airport to dinner here or there . That amount includes dozen+ of postcards, stamps, some of the tickets from and to airports at the beginning/end, some souvenirs etc.
Note that I always ate dinner outside, never cooked by myself and had at least one (mostly two) breakes for coffey, orange juice, tortilla etc during daily walk.
Dinners quality was not scaled with price
. Some at 8€ were just more than I could expect from any dinner, while more expensive ones (like one in Leon that I was invited to) were not so good (to quote friend who invited us, fellow pilgrims for his birthday dinner).
Recently, thanks to notes in the spreadsheet I've made some statistics.
So to the numbers:
Total spending: 1277€; divided into five categories: sleeping, food, transportation, dinners and other.
Sleeping/Albuergues: 254€ (36 nights, not counting prepaid one in SJPdP; I stayed only in Municipal, Xunta, Donativo etc).
Max: 20 (but dinner included); Min: 5; Avg: ~7,1.
Food: 514€ (lot of fruits and nuts, combined with tuna, salmon, yogurts for breakfast and snacks for a day).
Transportation: 14€ (some tickets from Bilbao airport to Bilbao, one from Santiago to the airport, for other I had paid before arrival).
Other: 158€ (postcards, stamps, tissues, soap and toiletries, washing/drying machine here and there, entrance fees, additional socks, some pharmacy stuff, souvenirs, offertory in a church).
Dinners: 337€ (including extra 35€ one in Santiago, one invited, and excluding two included in sleeping price etc).
Max: 13,5 (not counting Santiago one);
Min: 8; Avg: 11+€
IMO - writing it down the same day is the key. I prepared sample spreadsheet before departure (with basic functions as auto summation) and saved in the google drive.
Hope that will be of some help in planning.
--
Pawel