The biggest problem with shop costs is that a single common solider can be equipped much more cheaply then hero, and only advantage hero has in combat against common soldier is bigger health and slightly higher attack/damage due to stats.
Not to mention that hero health advantage stops being advantage after soldiers are grouped in parties of 3-4, increasing their survivability dramatically. Or if they gain level or two (soliders gain 3hp per level, 4.5hp if experienced, 6hp if veteran... and all that is for free, unlike heroes).
