I would look into two things. First, what's the annual profits? Revenues can be calculated by the number of cars (commercial and individual) passing per day, which will be dependent on population, frequency of passing (due to business and leisure purposes), its % share in cars owned, and the price. In terms of the cost, you can assume no running costs (so assume away any maintenance etc). Second, you need to multiply this annual profit by a certain EBITDA multiplier e.g. 10 years, to reach the company value i.e. NPV of this investment. So your selling price should be at least this value.