Formula vs baby- Similac Alimentum?

My daughter, 8 weeks old is currently on Good Start formula. We have tried numerous different brands, etc. For a while she did fine on Good Start but in the last few weeks things have changed. She has been throwing up curdled milk, much more than spit up and she doesn't seem to get full anymore. She is extremely gassy and constipated too. Today she had a sono to check her intestinal tract. Several people have suggested we try Similac Alimentum. The formula is outrageous in price. Has anyone had a similar situation that this formula has helped? I just want relief for her (and my washer!) :) Any suggestions/experiences are greatly appreciated.