I read enough bad reviews about this hostel online so I didn´t plan to spend a night there but then I couldn´t find the one I really wanted to stay. The tourism office at the bus terminal was closed at the time my bus arrived slightly after 5pm on a weekay and walked around the town under heavy rain without a map was a hell. Anyway, every budget traveller stay at Delicias del Ibera simply because it is the only hostel in Mercedes and they have a counter at the bus terminal that helps them to draw backpackers´ attention to their service..
A bed in a 4 bed dorm with bathroom costs 50 pesos (with HI membership 43 pesos) seems not too much but given the dirty and dim room with mosquitos around, I would say it only worths 35 pesos ( my 3 months of experiece of staying in hostels all over Argentina made me a qualified judge ). The kitchen is big enough, but without cutlery to use, luckily I carried a knife and spoon.
A lady who speaks English will come to the hostel at 10:30 and 19:30 to anwer questions about transportation to the Estero del Ibera and of course eagerly present you an excursion package, far more expensive than what you get directly from those hospedajes in Colonia Pellegrini, the nearest village accessible to the reserve.
I won´t recommend this hostel unless you have a fondness for mosquitos.