Samson Q2U Dynamic Microphone $58.95
Best pick for budget friendly (but very comparable to ATR2100 below per Spark Conference attendees). Dynamic microphones cancel out a lot of background noise because it is unidirectional and less sensitive than a condenser mic (ie. Yeti). Your host will be most appreciative.
These next two were recommended if you plan to host a show too:
Audio-Technica ATR2100X-USB Dynamic Microphone $91.92
This is the one I use. My son plays his video game loudly right outside my office and it doesn’t pick up a sound (unlike the Blue Yeti that captured it all).
Rode Podmic – This is the one the team at Spark recommends. A little more pricey I think.
Here is their guide with more info.