I don't know what you can do - but I have the same problem with my boy cat. He throws up all the time. I think it's because he doesn't chew his food well enough -- you can see that in his vomit. When he eats, he kind of inhales it. It really bothers me.. my female kitty doesn't throw up at ALL. She's only done it once because of a bad hair ball. But my other cat, she threw up a lot like the boy does now...and she lived to be a long healthy 15 years old.
Honestly..wish I had some advice, but I've just about tried everything. I've resigned myself to being patient and cleaning up puke all the time...
I'm using the same food you were -- the sensitive stomach food. As for price -- maybe you could mix a little bit of the older food with the newer food to help a little bit with the cost issue.