how much do microphones cost
The commercial kind are probably $250 on up. You can get a nice Shure brothers mike for around $120. Their SM-58 is good for recording and amplifying voices, and the SM-57 excels at recording or amping musical instruments. Sennheiser is a long-time company that also makes several lines of mikes (or mics, if you prefer) that range from home-use to phenomenal studio use.