Backpack prices depend a lot on size, fabric, and brand. Most backpacks cost between $99-300 USD. The medium-sized store brands generally cost around $199 USD. Store brands are cheaper than big-name brands like North Face, Osprey, and Gregory.
I don’t believe that any backpack is worth $300 USD, no matter how nice it is. These expensive backpacks tend to be large and have more bells and whistles, special padding, and material than you really need as a traveler.