My friend cancelled on me at the last minute, so I've taken a stab at payroll (support costs will follow).
If you go with the infantry organization I proposed, you're looking at just shy of 4.5M payroll per year. It's 100 personnel total, of which the equivalent of 10 are performing Admin duties (5 from the Medical Team, the Chef, the Doctor, the Lawyer, and half time duties from the CO, DropShip Captain, S-6 (dispossessed MechWarrior), and XO (senior Infantry Platoon Commander). I gave the XO the Veteran multiplier to boost their pay.
The more detailed breakdown is:
Salaries # Rank Base Officer Rank XP Pay Total Pay
Mechwarrior Captain 1 Captain 1,500 1.2 6 1 10,800 10,800
DropShip Captain 1 Captain 1,000 1.2 6 1 7,200 7,200
DropShip Officers 2 1LT 1,000 1.2 5 1 6,000 12,000
DropShip Crew 6 SGT 1,000 1 5 1 5,000 30,000
XO 1 1LT 1,050 1.2 5 1.6 10,080 10,080
S-2 1 2LT 1,500 1.2 4 1 7,200 7,200
S-6 1 2LT 1,500 1.2 4 1 7,200 7,200
Lawyer 1 2LT 1,500 1.2 4 1 7,200 7,200
Doctor 1 2LT 1,500 1.2 4 1 7,200 7,200
Infantry Lieutenant 1 1LT 1,050 1.2 5 1 6,300 6,300
Mechwarriors 3 Warrant 1,500 1.2 3 1 5,400 16,200
Top 1 MSGT 1,050 1 7 1 7,350 7,350
Senior Mech Tech 1 SFC 800 1 7 1 5,600 5,600
Platoon Sergeants 1 SSGT 750 1 6 1 4,500 4,500
Senior Medic 1 SSGT 750 1 6 1 4,500 4,500
Chef 1 MSGT 500 1 7 1 3,500 3,500
Other Techs 7 SSGT 800 1 6 1 4,800 33,600
Vehicle Commanders 3 SGT 900 1 5 1 4,500 13,500
Squad Leaders 8 SGT 750 1 5 1 3,750 30,000
Medics 3 SGT 750 1 5 1 3,750 11,250
Vehicle Crew 7 Corporals 900 1 4 1 3,600 25,200
Fire Team Leaders 8 Corporals 750 1 4 1 3,000 24,000
Troops 40 E-3 750 1 3 1 2,250 90,000
Totals 100 374,380
4,492,560