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".
BUT BP1 also grants access to pgrens and progresses tech as well as unlocking lmg42s, so it's not a flat cost for the rifle nades and can't easily be used to accurately inflate the cost of grens. At most we can attribute 1/4 the cost of BP1 into nades, so 25mp and 10 fuel, still putting them under for cost compared to cons. However I do not believe that ost teching should be considered into the cost of grens as it will be done and paid regardless if you use 5 gren squads or none, in contrast to conscript upgrades that serve no purpose if you don't build any cons and could be deemed cost ineffecient if you only build 1 or even 2.
I don't think it's fair to include the mobilize reserves unlock cost as it's an opportunity cost that can be mitigated via a full tech, so paying for it is a choice that shouldn't be included in considering their "price"