Aberdeen has a lot of guest houses. I stayed a couple of nights with a private room—shared bathroom—for 25 pounds per night. The breakfast was enormous! This could be about the same price as hostel, although it won’t have all of the social aspects. Think I found it with Smoothhound.co.uk

Ok so I just checked for nostalgia’s sake (it was ’06 if I recall) and found the one I used: Butler’s Islander Guest house. Looks like they’ve gone up 5 pound, but I’d stay there again. It was walking distance of everything. Smoothhound does list some singles for 22 GBP.