It is easy to spend serious coin on camping/backcountry, but you don't really need to buy anything to watch birds. Just your eyes and Merlin if you're cool with using your phone or your region's bird guide if you're not. If you want to make a thing of it, then, yeah, get nice binoculars with good lenses.

Something I learned from I-forget-where: if you hear an interesting bird call, close your eyes, look up and point your nose to the source of the sound. Open your eyes, and, surprise, it's probably a Northern Cardinal, Mockingbird or some kind of thrush! lol