You have not get the trick of sustainable combat. Guard + Bread it´s the trick.
You have two kind of encounters in a quest. Usually some ones +/- easy at the start, to wear you, and the last one with the final boss. In the first ones, kill all the enemies but one, a weak one if you can choose, and then expend some rounds making the Guard maneouver with all your team. Sure, the enemy will attack you and sometimes hit you, but all 4 of your character are healing and recovering MP for free, at a much higher rate. Use the Taunt maneouver to make the enemy direct attacks against the Goblin Layer, who have the most HP and defense of all your team. When you have made your team recover all/almost all his HP end MP, kill the poor fool.
And then use bread to cover the gaps and be again at 100%. You can start the adventure with let´s say 50 of bread stored. That will cost you only 250$. Each bread cures you 10MP + 1% of the max Magic points. Let´s say 11. With only 25$ of expense you can bring the Priest or the Dwarf from mid MP to full MP.
For refilling HP, it´s the same. More expensive, so while you are making the "Guard and Recover" you can consider casting some healing mirages. But still, 10 HP+ 2% of your max are easily 16-20 HP recovered per 5$ expense. You don´t need a lot of bread to put Anvil from mid HP to fully healed.
Save your expensive potions and tricks to use during combat. But the recover between combats, should be done with bread and the ocassional other cheap things that you loot.
Huh, interesting. Didn't even realise that the "guard" c0ommand restores hp / mp I usually never use that command in any rpg that has it unless it's a scripted battle where using it is a hard requirement and even then it usually just reduces damage taken a little bit which normally isn't fucking worth it. Will give your tactic a try.