Single serve packets?

I'm supplementing my breastfed baby with formula. I'm just not producing enough to be able to store breastmilk for her beyond the day I pump it. So some days, not every day, I need to give her formula. I feel like I'm wasting money on formula if I don't use up the whole dan within a month before I throw it out. The 2 oz ready to feed bottles are a good option since I only have to open them when needed, but they're quite expensive. Does anyone know about the single serve packets? How much does one packet if powder make? Is it more cost effective to just buy a whole can and throw it out if any is left over? My only option with the packets is similac since she hates the enfamil powder. She likes similac and gerber, but I don't think gerber makes packets. Does anyone know about packets?