Cereal?

Hey ladies! I was wondering if any of you experienced mommas know much about giving rice cereal? My son is now 8 weeks old but the last few days It seems I can't get him full no matter how much formula I give him. He's been eating 9-11 ounces within a 2 hour stretch almost every time he eats. I just feel like filling him up on that much formula isn't really the best for him not to mention it's crazy expensive if he's going to be going through it like that especially by the time he's 4 months old when they say you're supposed to start them on foods. Has anyone else ever dealt with this or know if it is ok to start a little bit of cereal at this age to help fill him up better?