Omnicef and insurance

My son was diagnosed with his first ear infection at 12 months old. He was prescribed Amoxicillin, but broke out in an allergic rash. We were then prescribed Omnicef ($50 WITH insurance!). He wasn't even on it for 24 hours and started vomiting anything and everything he put in his stomach. I gave him about a day to see if it was a stomach virus, but it continued. I called the doctor's office who told me to take him off the Omnicef and see if the vomiting continued. Within 24 hours, all vomiting stopped, so I called the doctor's office back and was given our 3rd and final antibiotic...Zithromax...which was the cheapest of the three.