I recall faintly there being a rule about repairs to vehicules costing 10% per box of damage.. So you'd be paying 100% of the price. But I think that's without street index, so it's still a good deal.
That's all I recall as far of official rules go, but I suggest going with a TN of the damage also, modified by good tools and etc as per found in the B/R tables, and a base time of Vey Long..
Second Edition? Man, get with the times!