"When I bought it new, the car was $1,100. Of course, it would have depreciated in value over the last two years from general wear and tear, so I'd say that at the time you crashed it, it was probably worth about $900. If you need to pay back $900, I'd say an interest rate of 5% is reasonable. That means that the longer you take to pay it off, the more expensive it will be, so I suggest paying as quickly as you can."

Yes, Andrew's put some thought into this.