Shampoo help please!!!

Hi everyone! So, I’ve never had the dream hair I want. In a sense, I know my hair will never be as full and voluptuous as I desire and it’ll never look as good long as I want because the ends are so fine and dry. For a few months now I’ve been allowing my hair to go 3-4 days at a time without a wash—which is crazy for me because my hair is SO fine and gets oily within like 24 hours of being washed—but I’m doing that because I heard that is good for building up a tolerance and also allowing the natural oils to do their work. I previously never used conditioner because it is too heavy on my hair and I didn’t need the added moisture, but during this quarantine I decided to really try and fix my hair problems and I’ve been using conditioner, too. I swear I know how to lather and rinse well, but I keep coming out of the shower and once my hair dries it appears greasy all over again within mere hours and it feels like the conditioner is still on it. I have a huuuuge sebum problem, as do most people with oily hair, but recently I scratch my head and there’s a bunch of white gunk under my nails. I know, I know, that’s super gross and I’m sorry—I promise I’m a hygienic person. I can’t fully tell if the white gunk is the sebum (bc that actually has been an issue before) or if I’m just not getting the conditioner out. I think the shampoo and conditioner I’m using right now might just be too heavy anyway. I took some online survey from this fancy shampoo company and they can create specialized products but it’s like $80!!! I desperately need a good shampoo that will finally CLEAN my whole head really good. My hair is so oily at the top of my head, and so dry at the bottom. It’s so frustrating. I’m attaching a picture (please be kind... I haven’t had my roots touched up in a while and this quarantine has me looking and feeling my worst!)

This is my hair 24 hours after my last wash.

Thank you in advance!

TL;DR

HELP ME FIND A SHAMPOO THAT WILL HELP WITH THE SEBUM BUILD UP ON MY SVALP BUT ALSO IS NOT INSANELY EXPENSIVE!!!