ABSOLUTELY you can do it. I agree with MANY of the restaurants others above have mentioned. Our personal favorites are:
Magic Kingdom
Casey's Corner - LOVE THOSE HOT DOGS!!
Pecos Bill - we actually feed a family of 4 for under $20.
Epcot
LOVE the Cantina in Mexico
Lotus Blossum Cafe if we're not in the mood for Mexican.
MGM
This one's tougher - we can't stand Pizza Planet - but we usually eat at the Commissary.
Animal Kingdom
Best value in the parks - Tusker House rotisserie chicken, just like some above mentioned. It's great!!!