Hi everybody,
IMHO there should be hard rules for item creation prices. Magic doesn't make a difference between a featherfall spell and an enlarge spell, both are first level.
Does magic know that improved invisibility is so much harder to make permanent than say Scrying (e.g. used for crystal balls).
So yeah, there have to be guidelines on how much would effect X cost and what spells could be used with X. There should be no possibility to cast a spell once per round. If you want it castable all day long once per round you pay a high price (per the DMG 2000gp is for 5 uses per day, we're speaking of 14.400 uses per day, that's 5.760.000gp times spell level times caster level).
Same goes for constantly active items. The price for them should be based on the duration of the spell. Say you want to make an item giving you permanent fly (duration normally 10 minutes/level) and one of permanent haste (I know very bad example... duration 1 round/level), youre a 5th level caster. For fly you'll need to prolong the duration only by a factor of about 28,8 - for haste by a factor of 2880, just to last it one full day!!!
Then there should be fixed costs for specific effects like armor bonus, attribute bonus etc. which override the other effects.
If you want to cast an extended bull's strength once per day on caster level 12 (lasts 24 hours) you pay X gp (per DMG 14.400gp = 3 x 12 x 2000 / 5). This spell would vary in effect for the usual 1d4+1 enhancement bonus to strength. For a fixed bonus you should pay a fixed amount like the table in the DMG proposes.
Perhaps we should try to make a better table than that in the DMG, one that has rules for nearly all non-broken spells.
Oh and btw the above mentioned hard rules should only be for calculating the creation cost of items, the market price surly varies by usefulness of the item. The Ring of Improved Invisibility should cost X gp and Y xp to create but on the market the price would perhaps be as high as ten times the creation cost.
That said, flame on
Greetings
Firzair