Hi
@Carrin and welcome to the Forum! As
@C clearly said, rooms in hotels/hostales/pensiones (and private rooms in albergues) are generally always priced per room and not per person. However, I have also seen a price given as a supplement for an "extra person", say if they put in an extra bed in a double room. I would expect that some places would do likewise if two people wanted to share what is priced as a single room. Not always, but I would expect that might happen. You may also find that some places will not allow two to share a single room, and in fact the single beds are quite narrow - much narrower than in hotels in some other countries - I can't imagine being able to sleep two in most of the ones I saw! In fact, double rooms (with two twin beds more common than a double) are by far the most common - you will find that many places don't even have a single room on offer.
Cost-wise, 30-40 Euro is a common price for a double room, sometimes with different prices depending on whether you want your own bathroom (some places have all their rooms with bath, others have some or all with shared bathrooms). But there is a great range - we paid as low as 25 Euro for a double with private bath and as high as.... well, that was for a treat!
Hope that helps!