Conscript and Grenadier have the same cost. They both cost 240. Conscripts is T0 units and grenadiers are T1 unit.
Soviet have the option to tech:
molotovs with a cost 80/10
At grenades with a cost 125/10
and after that mobilize reserves with a cost 100/20 (or get it for free with t4).
Grenadier:
require t1 with a cost 80/10
require BP1 with a cost rifle-grenades with 100/40
and they need T4 for reinforcement discount.
No matter how one wants to look at things conscript "spam" is more viable than grenadier "spam".
noone doubts that cons are the allround better unit (7th man is just the cherry on top)