Hi PicturePerfect - you can get a great new camera from a reputable dealer between $500 and $600. If the camera doesn't work, you can send it back. If you buy from Craigslist, in most cases, you're stuck with it.
As others have mentioned, the basic DSLRs in your price range are the
$547 Nikon D3200, the
$597 Nikon D5100 or
$588 Canon T3i. These cameras will do a great job for you, but they don't have some of the latest features (such as built-in wi-fi) and they are not waterproof.
If you plan to shoot outdoors or travel with your camera, you will run into rain or sand. With entry-level DSLRs, you have to worry about water or sand getting into your camera and damaging it. With a weathersealed camera, this is much less of a worry.
Pentax is a great brand, and makes the only weathersealed camera with a 100% viewfinder field-of-view in your price range. You can get the weatherproof Pentax K30 for
$579 in black or
$495 in red, for example. Here is what this camera can do:
Flickr: The Pentax K-30 Pool
And here it is in the field:
Or, if you want wi-fi control of your camera with your phone or tablet - and the ability to upload your pictures to Facebook or Instagram without waiting to get home - you might want to look at a brand new
$407 Samsung NX20 from BigValue via Amazon plus a new
$135 20-50mm lens from eBay.
Technically, this is not a Digital Single Lens Reflex (DSLR) camera, because it doesn't have a 20th century mechanical reflex mirror in it - but the sensor is the same size as in a Nikon or Canon APS-C DSLR, and it produces images like these:
Flickr: The Samsung NX20 Pool
And these:
Flickr: The Samsung NX20 Camera Pool
Most of the people in your class will have Nikons or Canons - I guarantee it. And most people recommend them on internet fora. These companies make great cameras - but that's no reason for you to limit
your choices to just two brands
Hope this is helpful,
Bill
Hybrid Camera Revolution