They're stat identical to an MG42- jacking their individual price up high would be a damn hard sell. Mg42, too, don't need any sort of a research cost- and commander specific unlocks never do.
It'd be pretty unreasonable to force either of those on the M1919.
It still is a bit silly that its a complete replacement of the BAR when it should be supplementary... and doesnt the lmg42 upgrade require battlephase 1? (But that doesnt mean much, anyways). Perhaps only riflemen should wield it as well - to counter its complete replacement of the BAR.