the SYHA Edinburgh Central hostel is between £18.50 and £24.50 pppn. Its about 5mins walk from Waverly station. They have singles, twins and larger rooms all ensuite with lockers. There is a self catering kitchen as well as a bistro.
Its a bit more civilised looking than the 20 bed mixed dorms backpacker hostels, unless things have changed dramaticly they don't do mixed dorms except for private groups and families.