Charity shops such as Goodwill and the Salvation Army can be a great source for knitting and crocheting supplies. I have purchased huge bags of yarn for as little as $5, sometimes containing expensive 100% wool brands.
Often when people downsize, give up on hobbies, or clean out a deceased relative’s home they often donate these supplies in one big batch.
If you are just taking up knitting or crocheting, eBay is a great source for used hooks or needles. People often sell them in a lot, so you can get a variety of hooks or needles for a fraction of the cost of buying them new.