Although some are more well suited than others, just about any modern camera can allow you to create very good photographs. At the $300 range, I'd simply look for something that allows full manual control (i.e. setting ISO, shutter speed and aperture), captures raw images (i.e. not just jpeg) and can accommodate an external flash. DSLRs are, by nature, more versatile, but may be out of your price range for even a used model when you factor in the cost of the lens (not completely out of the question, though).
That said, the camera is only 10% of the solution. The last 90% is the photographic technique and processing of the final image. You may already be fully aware, but the really amazing photographs you see from some of the members on here didn't turn out that way just because they've invested thousands of dollars in their camera gear. It's really because they've invested thousands of hours in learning how to use it.