If money is that tight, you might want to see if you can find a ready-made hat on sale.
Even if you find a free pattern, you’ll still have to pay for the yarn, and you’ll also need knitting needles or crochet hooks in the right size.
otherwise, I fully agree with orimono’s argument
but here, for example, a free pattern for a hat is offered
https://www.crazypatterns.net/de/items/834/einfache-muetze-schal-und-halswaermer-haekelanleitung
Simple Hat, Scarf and Neck Warmer Crochet Pattern
https://www.crazypatterns.net/de/items/473/muetze-indigo
Indigo Hat
but I don’t know whether that matches what you’re looking for.
I wish you lots of success with your hat