If 135 and 140fu is not very expensive, then why do you complain about Panthers price then?
By your standards, the cost is fine by the means of extrapolation of your logic.
Just asking.
Because teching factors into the Panther's initial cost, but you keep ignoring that.
To get a T-34/85 or a M4C, you generally buy T1 and/or T2, Molotovs, Anti-Tank Grenades. To get a Panther, you get T2, T2, and T4. In the below, I assume the Soviet has bought T1, T2, and both base upgrades.
90 + 260 = 350 (2 T-34/85)
180 + 175 = 355 (1 Panther)
While the Panther is clearly superior in the AT role, it lacks in the AI role and being outnumbered means it'll be on the defensive as soon as it hits the field.