Yeah, $300 is insane for a jar, light, live rock, and coral frag.
I think it's common to just use an air bubbler for O2, sometimes a heating pad depending on the lights, no filter or power head. Also common to seal the container to prevent evaporation (though I guess you need a little hole to let out the bubbles from the airstone). Some pico reefers dose, some don't, some do really big water changes like 100% every couple weeks.
Brandon Mason linked above has a great reef in a jar that's been thriving for a long time. He posts around here on and off, more on the nano reef forum I think, I forget the actual name of the site.
Mary Arroyo has a beautiful jar too.