Formula vs milk

So my baby just turned 1 in August he was born early so I was okay with leaving him on formula until his actual due date well now that has passed, it was the 17 of September, we haves tried everything whole milk, we even tried heating it up, we have tried soy milk which he seemed to like a little better but still not too much. So we have still been using formula which is too expensive so I am jut wondering if there is a trick we haven’t tried yet or just some advice. Thanks 😊