There is no correlation between a low bid and the best solution. Take a closer look at your low bid and evaluate the following:

The cost of asphalt is non-competitive and it is fixed at a set price across the industry.

If you know that pricing for materials should measure the same between differing bids and the costs of labor are similar. Then ultimately what is missing?

It is likely you are being shorted the necessary amounts of asphalt material actually needed for your specific paving project.