[@Phase Transit]Wiki states that Gandr doesn't cost mana but it does cost one's physical health. It's a cast from health type magic. 

I'm instituting limits based on these quotes
 [quote]Mana (マナ, Mana?) is the life force of the planet and exists in the atmosphere. It is produced by the world itself. Though Mana is usually found in great quantities, it takes a long time to replenish once it is used up. It is the primary source of energy for Nature Spirits.[/quote]

[quote]Od (オド, Odo?) is the energy found within living organisms such as humans and animals. Once depleted, the Magic Circuits that are stored in the human soul will begin to replenish it. [/quote]

The quotes say that they need to replenished. As such I put in rules regarding how many times a spell can be used. Emiya in Fate/Stay can only use up to ten or so of his infinite blade works replicate at the end of the anime which is how I'm gauging how much mana is supposed to cost.