Athletic shoes can not be waterproofed either. Calf-high work boots are a better option, but they generally aren't as comfortable as a hiking boot, can rub the Achilles tendon, and don't provide the kind of fit desirable for hiking. I recommend that you make the boot investment. Because even if you decide backpacking is not your thing, you can always wear the boots when you hike, shovel snow in winter, or mow the lawn in the summer. Your investment ultimately won't go to waste.
Feet change over time.
All those days your feet have been wedged into your favorite pair of Florsheims, Hush Puppies, or Nikes has caused them to change shape over time. Wear old boots on a long hike before you attempt a backpacking trip. You'll probably end up buying a new pair. The best boot for you, and the one you should buy, is the one that fits YOUR foot . It's really pretty simple.