I think one of the things people often overlook is the distance between the mic and your mouth. The closer the mic is to the source, the higher the signal-to-noise ratio will be, so the less echo and background noise you'll get. Many smartphone mics will sound very impressive if you hold them around 6-12 inches from your mouth. But you don't really want to do this with your hand, so it's important to get a mic with a nice stand or a form factor that allows you to comfortably place it where you'll get good audio.

Another thing people forget about is the noise canceling and other filters that are applied to your audio by default. If you're in a reasonably quiet place, it's probably reasonable to put "noise canceling" in Zoom on low. This will make your audio less garbled. If you have a really solid audio setup with headphones, you should try turning on "use original sound," which can make your audio really nice (unfortunately not available in Linux).

I highly recommend Fifine's mics. They have a USB condenser mic with a boom arm for $60 (~$35 for just the mic) [1], and a lavalier (lapel) mic for $20 [2]. The audio quality is really quite impressive.

[1] https://www.amazon.com/FIFINE-Microphone-Adjustable-Instrume...

[2] https://www.amazon.com/Lavalier-Microphone-Cardioid-Condense...