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.
Additionally, you’ll find that most travel backpacks are hiking backpacks, meant for camping and multi-day treks in the woods. Buying a backpack that was meant to be used in the Rockies instead of the streets of New Zealand doesn’t matter, though — backpacks are pretty interchangeable these days, and getting a backpack meant for the outdoors simply means you’ll have a stronger and more durable pack.