Good hostels in Mazatlan

Actually, there are no hostels per-se in Mazatlan. The Regis listed
above is not at all recommended (and a LOT more than the $8 USD cited)
Best bet is the Hotel Lerma at around $10 USD a night.

But better yet is nearby (like a 5 minute boat ride from the south end
of the Sabalo Centro bus line) Isla de la Piedra (Stone Island)

15 miles of beach with no multi-story buildings, just a few thatch
restaurants...it's maybe the furthest north you can have the Mexican
laidback island experience. There are two places to stay there worthy
of note.
Twin Towers (hard to explain....see the website) is what a
hostel-dweller would dig most, a camper/backpacker place with common
(open air) kitchen right on the beach with lots of fun company. Also,
the website is a good place to familiarize yourself with the Isla and
what it's like.
http://twintowers.mazatlan.com CHEAP!!!!!!

A little more money, but with private rooms, hot showers, etc. is the
Stone Island Beach Cabins operation, up by the (highly recommended)
Victor's restaurant. Just ask for Trini and Isabelle.
http://mexipost.com/isla

Neither place takes reservations or anything. Take a day trip to the
island to check it out and look at the lodging situation first hand.