Hi Andres,
Aside from staying off-site, the most economical way to stay at a Walt Disney World resort is by staying at a
Value Resort. My favorite value resort is Pop Century, but if you are traveling with little ones they may enjoy the theming found at the All-Star Resorts (movies, sports, music). All the resorts can be explored by visiting the above link.
I do want to also mention that
campsites are also available if you like camping, which may actually be the least expensive way to stay at WDW.
I'd also encourage you to visit
here as well as www.mousesavers.com to read about specials that can help bring the cost down, too.
Thank you for the question; please let us know if we can help again.