First, I don't think there is a replacement for a good mic. period. As others stated above the room is important as well but you can help that some with a decent reflection filter. (The foam doohickeys that sit behind your mic)
It's going to take some work to make a 300 dollar microphone sound like a modern day pop artists vocal chain. The good news is, depending on your ears, experience, music usage and standards, the word 'professional' is subjective and you may be able to achieve it quite easily with a SM 58 and some EQ.
Second - If you have high standards then a 300 dollar mic will probably not cut it in the long run, especially if you are comparing your recordings to modern music and are using 1 mic to record various instruments.
post edited by LpMike75 - 2012/03/28 00:23:41