There's only one hostel that i've hear of in Buenos Aires and it's always pretty full. Milhouses Hostel. It's very well run and has plenty on offer, but they charge a hefty price for it.
Actually there are a TON of really cool hostels in buenos aires. My favorites are Bait, Ayres Portenos, and La Rocca. The best source I've found to find good, cheap, backpacker/youth hostels in BA is www.minihostels.com. They have a whole network of hostels in South America plus in BA they also have restruants, tours, and language schools that they recommend. You can become a minihostels member for U$D10 and get a discount at all of their hostels plus the other stuff as well. Hope this helps!
There are really a lot of hotels to choose in this area. I don't know what price is too expensive for you, so learn the following info http://www.travelbraziltips.com/ I hope it helps you to make the right choice.
the garden house seems pretty nice and homey, and charges around $60 per person. The other site, hostel-inn, has a nifty list of hostel in buenos aires. Hope that helps!