now i wanna try some hair milk but i can imagine the labeling being expensive versus a shampoo/conditioner that just says it restores quality, never had long hair/split ends but the one time i did dye/and dry out my side bangs, some coconut oil worked fine
Oil and milk are used for different purposes. They can even be used concurrently if you got really badly damaged hair.
Generally, milk is for damaged hair or hair that's very prone to damage. It's meant specifically for hair repair. Oil is for preventing damage to your hair in the first place (particularly protecting from UV damage)
Both moisturize your hair as well, but oil is oil-based while milk is water-based.
Another reason to pick one or the other is the sheen/finish. Water-based moisturizers won't give an unnatural sheen while oil can make your hair glossier.
It all depends on what you're after.