I really don't either or the Men factions need a price reduction on their infantry. I'll go into both of them specifically.
Rohan: The only infantry Rohan has, excluding captains, are peasants. And peasants are already very cheap (150 for Normal Peasants, 250 for Farmhands). Not only are they very cheap, but the buildings that make peasants make money, and Rohan is the only faction to have that feature, except technically Lothlorien because of the Citadel and Beorning hut, but they have different money making mechanics then normal Resource Buildings. Keep in mind that the more money your farm is making, the faster peasants come out. So it would be wise to upgrade the farm(s) you are using to make peasants with Production increases, as well as using Theodens cruel taxes on them. Finally, Gamling can also just summon Peasants for free, which comes back decently fast if you Banish him with Corrupted Theoden.
Gondor: Gondor does have a lot more infantry then Rohan. However, Gondor Soldiers and Spearmen only cost 200 and 300 respectively, which is even with most other factions, and pretty cheap considering how effective they can be. And every other infantry unit (Tower Guards, Citadel Guards, Dol Amroth Soldiers), which are considered the elite infantry, already have a price reduction when you buy Town Houses (to 30% reduction if I remember correctly). And even if you think the prices are still too high, that's where Denethor comes in. His ability State of Emergency, I think after using the palatir 2 times, reduces the cost of all you soldiers, at the cost of making them less effective. And Finally, Gondor gets free infantry from the signal fires, which is very effective, especially with the Spellbook power that makes it better.
So, I really think that neither of the faction need a reduction like this. They both have their own means of dealing with the prices.
Don't take offense to my post though, this is just how I argue
. It's good to see people post ideas.