That's a pretty quick walk (5 days I think?) through some lovely country. You can get by on under 30 Euros a day. The food tradition in Galicia is simple food, so you will be right at home. Tasty and simple doesn't mean that you can't get a hearty meal if you change your mind and decide you need to do some serious calorie replacement.
Breakfast at albergues, if served at all, tends to be sparse. I typically skip it and grab something along the way (I'm partial to the fresh squeezed orange juice and pastries). In Tui, you can stop by the Convento de Clarisas and try the homemade biscuits and pececitos (little fish symbol cookies) for a few Euros.
Lunch is easily found at the cafes along the Way. Especially in larger municipalities, you can find a range of food, from simple bocadillos to more elaborate fare.
For dinner, it's much the same in most places: You can go with a simple salad (typically iceberg lettuce, tomato and maybe some tuna) or try out the local cuisine. Galicia has a variety of seafood, meats, cheeses and some great soup (and that's coming from someone who is not really into soup).
Tapas are a thing in Galicia too and you could make that your dinner if eating light (or not!). When in Padron (or anywhere you can find them), sample the Padron peppers (pimentos de Padron). You should try the patatas bravas (crispy fried potatoes with a spicy sauce) and pulpo a la gallega (boiled then roasted octopus -- I love it!).
Buen provecho!