Unit healing costs

Got another idea that can be executed in 3 different ways. Just throwing it out there for now, but might take it on later.

Right now the units magically heal themselves when idle, but what if there was some cost to it:

Suggestion 1:
It cost gold to replenish troops/weapons/repairs
1 gold for each hammer healed. If no gold, no healing.
Formula %ofDamage * #ofHammers so a 30 unit that is 50% damaged will cost 15 gold to fully heal.

Suggestion 2:
It cost hammers...
2.1 : The production is automatically lowered some % equally in all cities and the difference between lowered and 100% is calculated into hammers which is used to heal.
2.2 : There is a new production similar to build wealth/science/etc that produces Supplies. Whenever a unit is healing, hammers are taken from that stack of supplies.
2.3 : A global rate OR local rate can be adjusted in % and the % is lowering production in cities and whenever a unit heals, it is taken from that stack.

Suggestion 3:
3.1 Culture from the hometown of the unit is being converted to healing. Maybe not a good idea considering its quite common to have majority of units from same town.
3.2 Culture is taken like S2.1

any other suggestions?

actually units heal themselves ridiculously slow (specially if you play on Marathon speed and in enemy lands), unless you have Medic promotion.

What I did in my mod, I removed Medic promotion and instead you must build supply train to support them - just like in Charlemage scenario.