Which mercenaries book are you working out of? There's a few different ones I know of, there's the older Classic Battletech Field Manual: Mercenaries and Mercenaries Supplemental books, and then there's the newer Combat Manual Mercenaries with the redone artwork for the Warhammer, Shadow Hawk, Griffin and Marauder on the cover.
The Field Manual: Mercenaries has a table on page 148, page 156 using Adobe Acrobat Reader, that has multipliers to raise or lower a persons pay depending on their level of skill, from Lowly Assistant with a 0.5x multiplier to an Elite Pilot or whatever with a 3.2x multiplier.
I recently went about building my own Mercenary unit and calculated how much it would cost, salary wise to pay everyone from the Aerospace pilots all the way to the Technicians and it came out to somewhere around 14.7 million C-Bills a year. Now that was using the "base" salary given in the Field Manual: Mercenaries book, where people like Mech and Aero pilots make 1,500 C-Bills per month, which comes to 18,000 C-bills a year.
If I were to drop some of the pilots and other people such as tank crews and infantry down to the "green" level, that saves me 40% over the "regular" level pilots.
So that mech or aerospace pilot that makes 1,500 C-Bills per month goes down to 900 C-Bills a month, 10,800 a year.