Our Spanish adventure started in Bilbao (which was a lot easier than diving head first into Madrid or Barcelona) staying at the Gran Hotel Domine (an RS splurge immediately across the street from the Guggenheim). Their rooftop breakfast was good but the menus were (really) pricey IMO unless you’re going to eat everything you get with them (€15 and up and up).
Ordering a la carte works better once you know what you’ll actually get. The café (€5-6) is for a carafe (“termo” 0.5 litre) of good dark coffee. Order a “café blanco” and you may get another carafe of milk (and probably more than you bargained for at similar price). Zumo de naranja (orange juice) also comes by the small pitcher (“jarro”). Hotel guests also get a free small shot glass of their “calming juice” (orange and kiwi fruit?). From there my wife chose (more wisely) the other options.
This still will not make for a “cheap breakfast,” but you will have The Guggenheim Bilbao (and “the puppy“) at your feet and the rest of the hills to view while you start your day.
Why there are no evening options - even just drinks - is a question for management. Perhaps rooftop dinner and drinking hasn’t made it across the pond.