One question you need to figure out is, is he refusing the bottle because he doesn't like bottles, or because he doesn't like the taste of formula (have you tasted it? it's really gross compared to breastmilk, which is sweet).
If the bottle's the problem, he's plenty old enough for a sippy cup, so just find one that he likes. This is actually a good thing to do anyway because then you won't have to wean him from the bottle later on.
If it's the formula, you can try mixing it with breastmilk and gradually increasing the proportion until he takes it.
Either way, consider that if you can just hold out for another 2.5 months, you won't have to deal with $$ formula at all and can just switch him to whole cow's milk. I found that once my son was down to nursing 2-3 times per day (morning, after work, and before bedtime) it really was no effort at all for me, and actually it was really nice because as he got busier and busier it was the only snuggle time we really got.