This is not as ridiculous a question as it sounds.
This is not a power gaming question, or an attempt to bypass rules. I am not a player in anyone's game.
According to the item creation rules, IIRC, an item with a magic ability usable 5 times per day is equivalent to an item that has unlimited used per day. So as written, a fire ball "gun" that has infinite use per day is the same as 5 uses per day.
Having said that, clearly there are exploitations. Mage armor built into a wondrous item could be made for infinite uses per day for only 2000 gp IIRC (sorry AFB ATM), maybe only 1000, but bracers of armor cost considerably more.
So as the "average spell" goes (meaning nominally useful spell, not the actual average spell, create water and 'scribble message' don't count), what is the value of an infinite use of any given spell for a character?
By value, I don't mean strictly gp. I also mean in terms of character resources. I'm being somewhat vague because I would like people to respond with their opinions and not be constrained too much, but please feel free to define you values and definitions as need be for your points.
I should say I'm mostly concerned with sorc/wiz spells, but all spells are up for discussion here.
One example: in the 3.0 days the savage species book had the ghaele's as a class-style progression. around level 8 the gheale characters could cast cure light wounds at-will. This always seemed terribly unbalanced to me, but the ghaele did have some serious disadvantages. This is a similar kind of situation that I am contemplating.
Thanks for your time folks.
