Nice concept! Some suggestions:
- Currently, shields and heal are almost the same, I would consider that the player's shields are only worth for the current attack (that is, what is left over is lost). That would differentiate more both actions, and also would make the game more tactical. In the case of enemies I don't know if it would work the same way.
- Make it possible to consult which die is which, among the ones you have rolled, so you can choose wich one to roll again. In many occasions you can't tell just by looking at the visible faces.
- Another way to balance the multiplier faces can be to make their price rise (double?) with every purchase (and probably you dont need the x4 option).
In any case, good luck with the final game, if you make it.