2001 Hyundai Elantra inspection

OK a month ago, I was low on gas so I got gas five minutes from work. When I left I noticed it still said I had no gas and I had gotten like 3 or 4 gallons and then the check engine light went on. I got more gas the next day...enough to fill me up. It still said I was empty. The next day after that I drove to a friend's house and it said I had a full tank. I had an appointment for the mechanic for the check engine light the day after that. The morning of the appointment, the light went out. Occasionally when I got low on gas, the check engine light would go on and then after getting gas the light would go off. The light hasn't stuck around long enough for me to get it checked out when I had the money to check it out. It stopped after a while.
I got my car inspected the other day and I failed for the check engine light. (Which wasn't on when I went in and hasn't been on for weeks.) The codes were P0302, 456, 507 and 100. Anyone have any ideas how and if these codes are related and roughly worse case scenario how much this job would cost?

Please send an email...not a post so I would be more likely to check....ane8008@gmail.com

Thanks. :)