Milk storage in ziplocks? Input plz! 🍼

I’m a new FTM. 3 weeks in and our freezer is full of breast milk canisters from pumping. (I have a preemie so I’m strictly pumping)

Another method is to store in ziplocks and stack in freezer.

Can you please tell me:

a) how much this costs you monthly?

b) is it worth it? i.e. it looks like it could spill everywhere.

I use a Medela pump. Thank you for any input. I’m a little overwhelmed. 💙🙏🏻