Recruitment Rank and Cost Reduction passives stack :)

[Pimpin Pippin]

In my last few campaigns i have been using this neat little tactic:
- at start have 1 or 2 armies of the cheapest units while focusing on your economy, city development and trade
- get 3 heroes (or 2 heroes + 1 lord) that have the Unit Recruit Rank and Unit Recruit Cost passive skills
- put them in the same province where your main unit building structures are and recruit an army

Any army unit you begin recruit will automatically become Rank 9 and will cost you 45% less gold to purchase (upkeep is unaffected).
The best part is that your heroes are only needed in that province at the moment when you are purchasing the units.
Then your heroes can leave that province and do whatever wherever while your army that is being built will be rank 9 and at 45% cost discount.

My typical method of using this tactic is from the start to focus on economy while fielding 1 or 2 armies of the cheapest units possible to defend and expand and establish trade.
After my economy is up and i can make higher tier units and enough adequate heroes i will start "replacing" my cheap armies with high tier rank 9 units at 45% cost discount.

Raiding/sacking/pillaging with your cheap starting armies is a great way to fund your economy and city development, especially if your race has gold bonuses to those actions (like elves).
As soon as your high tier rank 9 discount army is made everyone near you will behave and not want to challenge you.

Not only is this a great way to make a max level army at a very cheap cost, but it also means that any unit you might lose can be replaced with a max level version of it for the same cheap price.
If you want you can stack the recruitment cost discount even higher than 45% but the military units are capped at rank 9 (which is a nice bonus to most stats a unit has).

[Ysthrall]

This is indeed a useful strategy. The AI uses it quite a bit as well, which is why you run into Chaos armies with lots of hiogh level units...

[gachi is manly]

Upkeep costs are the important factor, IMO. Recruit cost is easier to ignore with a strong economy than Upkeep costs, which is more of the direct limitation to your overall army size.

Unit recruit ranks are a great skill but I wouldn't waste points on recruit cost. It's especially easy for races like Wood Elves that can get the +3 unit recruit ranks on their fresh Branchwraith recruits with the proper tech/buildings.

[Pimpin Pippin]

Well for some units that cost 2000+ gold having a 45% discount is rather nice :)

Yea of course the upkeep is much more nasty but we can not affect that by stacking skills (as far as i know).