Preserve the input voltage range while reducing part count for a power supply
I was thinking of using a 7805 that just needs a input and output
  capacitor


If it could run from 40 volts then the device would drop 35 volts at a current of 0.8 amps and dissipate 35 x 0.8 watts. That's 28 watts and to be largely avoided as a design idea. You need to concentrate on switching regulators because of their far superior power efficiency.

Here's a design that uses 8 parts: -




  BOM count of 24 and this needs to come down to not more than 5


I suspect that small board area and low power dissipation might trump BoM count.