Engine Problem: Suggestions for diagnosis, please

Car: Hyundai Tiburon 2001
Mileage: 109,457
Engine Size: 2.0L L4
Automatic Transmission

A few days ago, I had my battery replaced and I was in the middle of my commute from work when my engine began to vibrate and shake the car pretty violently. The engine light will blink on and off, and sometimes it will remain constant without blinking, but after 30 seconds or a minute, it will begin to blink again.

I have not driven since the problem. And, I did notice that the vibrating/shaking stops if I am above 30 mph.

Has anyone else had this problem? Do you know what would cause this?

Is it expensive? I ask this because I have begun the process to buy a new car and trade this car in. Thanks!