There are three great low-cost microphones you can use when starting a podcast. We recommend the Samson Q2U: it's a great-sounding podcast microphone. It has a USB output for easy connection to a computer, and it also has an XLR output for use with an audio interface. The Audio-Technica ATR2100x-USB is another good option (and has both USB and XLR outputs). If you have a bit more money, we recommend the Shure MV7. It's a pro-level dynamic mic with both USB and XLR outputs.