Both of my boys self-weaned totally to bottles when my milk started drying up at 4 mos. We just used the basic Walmart bottles-no fancy brand names, couldn't afford them, & they were just fine. Our older son tried his first sippy at 12 mos & threw it across the room. I weaned him down a bottle a day until he was totally on the cup (about 14 mos-he was on formula that long too), then weaned from that to the straw cups & regular cups. Our younger son wanted to be like his big brother, but he too threw the sippy the first time. Turns out, they were the leak-proof & drink-proof ones, neither boy could suck enough out at first so they gave up. I bought the cups that weren't really leak-proof w/just a rubber slit in the top of them to start drinking (again, just from Walmart).
Keep taking the bottle to daycare, but make sure they know it's a last-resort. Tell them how long you want them to wait before trying the bottle, so they don't fill the cup, offer it & get rejected once & then move to the bottle right away. It's your baby, not the ped's, as some mommies have said. You do what's right for him, books be ... um, yeah... He won't start high school w/a binkie, he won't get married w/a blankie.. they're only babies once, go by what your family needs/wants, not by what the book or the doc says always.