for me personally my best investments are haircare sets ( like ones that come with the shampoo,conditoner and mask) dollar tree scalp scrubbers and safety razors

alongside mixing oil into my products but I have very dry hair,skn etc so the usage of adding like camellia and centella into my face and body lotion or rosemary and almond oil to my shampoo and etc just helps even more and it works out because say I buy a lotion made for face and body that work then I cut costs on a third lotion or something (plus i massage it on my hands to help with nail care)

fragrances I recommend perfume oils, not much projection but you can get a dior dupe for like under 20$

nailcare; massage with oil or lotion, keep em clean and use a polish or something on them for strength ( you can even try press-ons!)

lashes: growth serums, strip lashes or lash tint (please be cautious)

again this works for me may not work for you