Storing milk in bottles or bags?

I'm looking for the most cost efficient way to store breastmilk. Bags are obviously the easiest however bottles seem like they would be more cost efficient because they are reusable my only concern with using bottles though is how many would I need I plan on breast feeding naturally and pumping but I have inverted nipples so I fear I will end up just pumping. Just wanna make sure I have enough or at least close. Thinking about buying a few bags to store some milk for long term and maybe only using the bottles for storing in the fridge. Im still learning about this so go easy lol no snippy comments pls tia mama's 😊