The Pro-Ject will probably be a good move, then... it's at the top of your budget but will be convenient.
Going from the Numark or other cheap-o's to something like the Pro-Ject w/ its included cartridge will make a noticeable improvement in playback quality.
However, using an old turntable with a good cart, connected to the receiver, etc. might sound as good or better during playback.. I'm not sure about the digital conversion differences, though.
Converting vinyl to mp3 makes me want to cry.... However, the convenience is understandable... So, at least do a .wav and convert to .flac. pretty please...
Otherwise, I doubt you'll hear anything analog about it other than some compressed clicks that represent the scratches and pops.
-C