Im considering going this year and looked at the badge prices and saw Sunday badges were significantly cheaper at 18$. Is it worth it to go on Sunday, or will things be sold out and deserted? For context, I live one state over so travel costs aren't too bad.

Yes, it's worth it. Sunday is a short day, but it's the full experience up until 4pm.

Personally, I recommend anyone who hasn't done it to do a GenCon Sunday. The dealer's hall alone can take up an entire 10-4 day.
Cavaet: You WILL end up wishing you had come for the entire show.

Thanks for the replies! I have an additional question. Are all game demos listed under events or can you do them in the exhibit hall?

There will be a lot of demos in the exhibit hall.  You could spend the entire convention doing demos there.  But, these are generally limited to a couple of turns only, whereas a demo event listed in the event catalog would be a play through the entire game.

This is my advice after the FUBAR will call that I saw last year. If possible come downtown Saturday afternoon or evening and pick up your Sunday badge. Last year there were long lines of families waiting to buy or pick up their 1 day badge. They lost a lot of time in line. 

Sunday is only worth it if you want to go to the Dealer Hall.  That's why it's so cheap.