I concerned about the cost of running #6 wire/ for a 3ph 50 amp disconnect. I know wire cost has increased substantially within last year or so. What should I expect as a cost for a job of this type-5-6 hours---30-40 feet run?

Based on the information provided, the best I can estimate is $500.00 to $1000.00. I could get closer to an more accurate estimate if I knew what type of wire, copper or aluminum, what type of raceway, EMT, MC cable, Romex, Is the disconnect fused or non-fused, 250 volt or 600 volt.

What area of the country are you in?

My point is there are many variables to electrical work, many choices available for types of materials. And the more detail given to provide the scope of work will result in a better more accurate estimate.