How much are they going to cost post-Patch in JP? I forgot to check last time I was on the PTR. Champion's Seals cost seems to be the same.
Champion Seals are not changing at all since they are a unique currency. So those prices won't change.
Heirlooms on the PTR..
2175 JP for chests, shoulders, and one handers.
2725 JP for the spell mace and trinkets.
3500 JP for two handers and the bow.
So in other words, shoulders right now cost 40 heroism which equal out to 40 high-end emblems due to the 1:1 down-conversion. 40 emblems once the conversion occurs with be around roughly 460 JP.
So think of it like this... Let's imagine you are using both Triumph and Frost Emblems for the down conversion, and that you will get roughly 5-7 emblems per heroic.
In the existing system, 5-8 heroic runs will get you the shoulders.
After the conversion (1 emblem = 11.5 JP), you would need roughly 190 emblems to get the same item. That's 27-38 heroics or so.
After the conversion is over and we are running the old heroics for JP, it would be around 87-119 per random heroic. That means roughly 20 or so heroics give or take some, I am not really trying for hard math here.
It's much better to get them now rather then wait for the conversion or farm after the patch.