The most important thing to consider is that the beauty of Sagas is that they are optional extra rewards and should remain that way. Hence they cannot reasonably be the main route to earn Hearts.
The second thing to consider is the Hearts for heroic TR is currently fairly easy to acquire and making that several magnitudes harder will be seen as a huge nerf.
The third thing to consider is the epic and iconic Hearts are new and hence much more open to being hard to earn to make store sales look appealing to some players.
Finally I will assume that the tokens of the twelve are out of the question for some reason and that the new vcoms have to be used even for heroic Hearts.
Make the end chest in every epic quest drop vcoms. 1 on casual, 2 on normal, 3 on hard and 5 on elite.
Make epic raids drop 20 on normal, 30 on hard and 50 on elite.
Change the cost of the heroic heart to 200. This is still much slower than getting 20 tokens currently but somewhat within reason.
Keep the costs of epic and iconic Hearts and the saga rewards at the level seen on Lam at the moment.
The cost to earn a heroic Heart goes up but not by all that much and you are not locked into a specific set of quests.
The cost to earn either an epic or an iconic heart means running quests in excess of simply getting the 6.6 mill to get to 28 and the Karma needed in case of an epic TR but not to an impossible degree. Further running EE is promoted and Sagas remain optional and hence positive.
Running lots of different raids is significantly promoted as a means to get vcoms but still very much optional.
In all cases this means there is a reasonable choice between the convinience of buying the heart from the store or farming it out.