Starting in Lisbon, i dont know, but starting in Porto: If you walk the stages from, lets say, Brierleys guidebook (not a must, using a guidebook), you will always find an albergue, municipal or private. Prices will be from donativo to aprox 10 euros.
I believe that if you walk from Porto to Vila do Conde (the first day allong the coast out of Porto) there is no albergue in Vila do Conde. So you would have to find a b&b, hotel ect.
Of course this will be more expensive then an albergue (25-35), but avoiding to walk out of the centre of Porto to Vilarinho is well worth it. That walk is awfull an can be pretty dangerous and i dont say that quickly! Please dont do this, or at least take a bus/metro out of the city.
Portugal for food and drinks is (much) cheaper then Spain, but i think if you calculate aprox 30-35 euros per day for breakfast lunch dinner, some drinks and a bed you should be fine.
A coffee allong the way in Portugal can be as cheap as 0,60 cents. In Spain 1 euro is average i think.
Then a percentage of road walking? Pfjew, i could not put a number on that. For me it was not enough to get annoyed by. I guess thats the most important thing (?).
Maybe somebody else can put a number on it. I did find some of the road walking dangerous, now and then, but i also thought this about the Frances now and them.