1510-300 = 1210. Don't forget the starting sturms.
You dont think the starter unit in the game comes for free, do you? The more expensive your starter unit, the less manpower you start with.
Btw the reinforcement cost not supposed to reflect the AT potentials of the unit. There are other values in the game, not just the AT. The 90 munition / schreck upgrade price reflect how well the squad perform against vehicles. The reinforcement cost is calculated somehow like this: (units price / squad size ) - 30 = 1 model ... or something like this...
And again, if you make an example where your opponent has a SP, 4 volks and a kubel... dont you think you should have something more than just 2 hmg?
There is no such thing as OKW manpower hack..