2005 Jeep Grand Cherokee won't go into Drive

Hello, I was driving my Jeep Grand Cherokee for about 20 miles this morning. It has the 3.7L V6 4x4 w/ about 127,000 miles. I came to a stop at an intersection and when I went to accelerate again there was a loud bang and shudder from underneath the hood like I had hit something. I stopped immediately and it wouldn't accelerate at all. I turned the car off and on and it started up just fine. Then I tried to put it in Reverse and it just made a whining noise. When I put it back into Drive it just wouldn't do anything. This happened at the worst intersection imaginable with an officer behind me so I had to have it towed right away. Just wanted to see if I'm looking at a $3,000 blown transmission or if these might be a cheaper clutch or differential issue. Any help would be greatly appreciated.