So I responded to a post earlier to clarify this for someone and I will do the same here.
Here is that post and it also shows the location of the altars:
You can learn all 3 religions up to Tier 3 for only 63 Points in total.
Learn one religion by default at the beginning of the game. Easy part, 1/3 the way there.
Make the trip to the other two priest and click the middle option on their dialogue screen to become an acolyte of their respective religion. Congratulations, the second hardest part is over. No make the altars and use the ritual weapon to have the main benefit of each religion.
Once you level up and have the skillpoints you can get the upgrade to the tier 2/3 altars but this is unnecessary if you just want the standard benefit from them. However if you want to summon an avatar you will have to decide to upgrade one to max tier 3 and slap a priest in there.
Here is where the confusion comes in. When you see the slillpoints before you purchase the altars it says 50 points. It is not.
Once you have the acolyte level, tier 1, the next level is 10 points, tier 2, and once you purchase tier 2 the next level, tier 3, is 11 points.
Tier 1 = Free (must make the trip to save 50 points)
Tier 2 = 10 skillpoints (each)
Tier 3 = 11 skillpoints (each)
This makes the total skillpoints invested to be 63 points total for all three.
I have done this twice now and have had enough points to still get all the end-game items like the explosive jar, vault and other stuff.
Now when you go out you can choose which ritual beat stick to take with you to stock your gods’ coffers.
Set – You can get some hearts so you can make anti-poison for spider caves.
Yog – Yog biscuits for that health re-genning, unspoilng food. This is the real mvp.
Mitra – Ambrosia so you can have another regen item along with the aloe. Mitra also gives you a well so you save points with that.
Keep in mind that you can’t have altars too close to each other so your base can’t be small to do this. This also applies to the well that you can craft from Mitra.