Seatbelt broken after minor fender bender?

I drive a 2010 Honda Insight, and was in a really minor wreck about a week ago. The seat belt was fine at first and the air bags did not deploy but the "check airbag system" light came on afterwards. Yesterday the seat belt came all the way out and won't wind back up, so its very unsafe. Is there a way to fix it myself, or do I need to take it to Honda? Do you know about how much it would cost to have fixed?