Professional usually means that you plan to make money selling your pictures.
But that does not usually go with "not too fancy and expensive".
For professional usage - the minimum price for a camera is around $700.

If you just want to get serious and learn more about photography, you can find many excellent cameras for around $300. You want a camera that has some manual controls like shutter priority, aperture priority, and full manual. That lets you learn how to control exposure.

All digital cameras are easy to understand when you use them in Auto mode.
To be more creative you need to get out of Auto mode and take control of the camera.
Auto mode is a compromise that works well most of the time, but for those difficult situations you need to know how to get the best performance out of your camera.

Here is a link to a short course in camera usage:
http://www.shortcourses.com/use/

Give us a better idea of what your goal is.
Let's start by how much are you expecting to spend on your new camera.
Then we can better suggest a camera.

..