You're going to be spending a lot of time with that yarn you're considering.
It's worth it to spend more to ensure you love it.
One of the joys of knitting comes from the giddy delight beautiful yarn brings. Granted, beauty is in the eye of the beholder, so my love of bright colors, speckled yarns and softness might not be what makes you happy. Maybe you love a squishy, chunky yarn, or love to knit like Kiana does, on tiny toothpick-like needles using lace weight yarns. But that's just it: your time is worth a lot. Use yarns you love.
Generally, in my corner of the knitting world, yarn should be made from natural fiber: merino wool, alpaca, cashmere, cotton, and the list goes on. My grandmothers and great aunts all used synthetic fibers, acrylic, which was washable, abundant, and inexpensive. When you go to a big box craft store these days, they sell acrylic and acrylic pretending to be natural fiber. Read the labels. Yarns labeled as alpaca may contain only 5% of the soft goodness, when for a small step up in price, you could buy an alpaca wool blend, or heck, even pure alpaca from a yarn purveyor.
As a child of the 70's I know the plastics based economy was awesome in many ways. I just don't want to wear plastics, or dress my kids in them. Not when natural alternatives are so abundant, SOFT, and colorful. Acrylic yarn is plastic and requires lots of nasty chemicals and dyes to make it soft enough to spin into yarn. Most crafters can only access or afford this yarn and it has its perks. But, if you can, and if you already put a premium on reusable bags, organic food, and soft clothing, you probably want to be a yarn snob like me and go with natural fibers. Yarn snobs are always welcome here.
Yarns to love knitting:
And so many more. Which yarns do you love to knit?