Hi Kate.
You can view our demo site if you ever want to refer to how things should be acting: http://wpshindig.com/events/list/
However, I’m not sure any of the events there have a cost, so I tested on my localhost and the /wp-content/plugins/the-events-calendar/src/resources/css/tribe-events-full-mobile.min.css file has this rule:
.tribe-events-list-separator-year,
.tribe-events-list .tribe-events-event-cost {
display: none;
}
This file only loads for max-width: 768px, which is why the cost is not hidden on desktop.
Your site may be loading a different CSS file depending on your “Default stylesheet used for events templates” option at wp-admin > Events > Settings > Display tab, but I think it’s safe to say it’s probably always been this way for all stylesheet options (just my guess).
Please let me know if you have any follow-up questions on this topic.