Bless your heart....I've been there. When I was first learning to knit, I searched on eBay every day for box lots of yarn that people were getting rid of. I was thrilled to get HUGE boxes of yarn for a great price. Even though some of the yarn was old, there were still some treasures hidden in the midst of it.
You can get yarn at thrift stores too, or Salvation Army or Goodwill. Believe me, I've gotten loads of yarn there! Now, I am finally able to buy a few new skeins every once in a while, so my stash is getting too big! Let me know if you want me to mail you a box of my skeins from my earlier days. I'll be glad to share some of my worsted weight stash!
For the first pattern, you can use any yarn. 2 strands of worsted or light worsted or DK yarn....whatever you want. The hat will just be thicker or thinner, that's all. I used Red Heart worsted weight for the grey hat. I made another hat later with Lion Brand Wool-Ease worsted weight, which was a softer yarn, and it was a little easier to knit with.
For the second pattern, I usually use Lion Brand Wool-Ease, but any worsted weight yarn will work. I like to have a few different colors of the same brand so I can make stripes. A wool blend yarn is better than 100% acrylic for making hats, since they get so much wear. Otherwise, they just wear away and get full of holes.