Started typing this for Creedrow, and concluded Ornn would need this info, and maybe future players too, so i'm putting it here.
Disclaimer, this is a lot of 'talk' and it still not all the rules, since there are limitations that i'm not going to go into, but they exist so you can't just take these rules and min/max power game with them. They're a guideline, not the absolute rule on how things work... VERY IMPORTANT for players to acknowledge that take crafting feats for magic items.
There are house rules on what can go in what, and as a general only one spell per item.
ie.
Boots are used for movement based spells, like expeditious retreat.
Gloves are used for spells that require the use of hands or touch, like shocking grasp or lay hands.
Rings and Necklaces are general spells and are a sort of wild card in that they can take any spell. (It helps to justify the feat specific to forge rings, since they're limited to two body slots).
You can only 'attune' to 'one' item per slot too, so you can't have a bag of rings, to use... put away, and put on a new one.
This concept has been throughly thought through for abuse.
Cost for Imbued magic items are actually from the core rules:
Level of spell x Caster level x 2000 gold pieces / 5 (1 use per day) = 400 gp for a level on spell cast by a level one caster, plus the cost of master work item. That's pretty inexpensive for what it does, but i work in a low magic/income campaign so that works fine.
This method accounts for 75% of the stuff that shows up in the campaign
The other way type is i scale down magic items, i scale down the effects and the cost for something. ie. The pouch of holding is based on the bag of Holding.
25% of the stuff that shows up will use the scaled down method
Scaled down:
Original Item
Bag of Holding Type I
weigh 15# capacity 250# Volume 30 cu' Cost 2500gp
New Items
Large Pouch of Holding (20% of bag stats)
weigh 3# capacity 50# Volume 6 cu' Cost 500gp
Small Pouch of Holding (10% of bag stats)
weigh 1.5# capacity 25# Volume 3 cu' Cost 250gp
This is used for wands too, so some 'fully charged' 'expendable' wands in the campaign will have less than 100 charges. Really a 100 charages is over kill.
The scaled down method has also been applied to staves.
The normal cost for a staff is pretty obnoxious to the point that you never see them, and in the scale of my campaign impossible to consider.
The core rule cost of a staff are...
1st slot - 400 gp x caster level x level of spell
2nd slot - 300 gp x caster level x level of spell
after 2nd- 200 gp x caster level x level of spell
Caster level was 'no less than 8th', so the cost of that first slot was going to be at least 3200gp x the level of the spell (more if it was a spell that an eight level can't cast)
You EASILY break into the five or six digit cost for staves under these rules.
So how do we make the cost more in scale with this campaign...
First, acknowledge that the highest level spell a character will normally have access to is 3rd level. I can count the number of third level spells that were actually cast in my twilight campaign on one hand. (One fireball and a few haste)
The campaign limted class levels to 7th at the time, but they've now been increased to ninth (with the caveat that spell levels are limited to third)
You could learn craft staff with a 6th level caster class. Minimal Caster level is reduced to 5th level. These are reasonable scale downs, when you consider that the highest class level is 7th, and the highest level spell you have access to is 3rd.
With these tweaks, the cost of the first slot is reduced to 2000gp x the level of the spell. A nice price break, but still beyond the scale of the campaign economy.
Then we tweak the forumula. The Core rules, presume that the max charge of the staff is '10', but what if the max charge of the staff was fewer. What if we tweak the cost based o n the charges the staff has? This will put the cost in line with the campaign...
So... this is the forumla used from the above logic.
1st slot - 40 gp x caster level x level of spell x max charge of spell
2nd slot - 30 gp x caster level x level of spell x max charge of spell
after 2nd- 20 gp x caster level x level of spell x max charge of spell
So... running the numbers. Lets say we want a cleric staff. We want it to have Bull Strength, Bless, and Cure Light Wounds. We're willing to accept that Bull Strength will take two charges to use.
Using the Core rules, the cost will be.
Bull Strength 400 x 8 x 2 = 3200gp / 2 (for 2 charge to cast) = 1600gp
Bless 300 x 8 x 1 = 2400gp
CLW 200 x 8 x 1 = 1600gp
Total cost = 1600 + 2400 + 1600 = 5600gp not a terrible cost for the typical campaign, but... still steep in the scale of my campaign.
Using my campaign rules the cost for the staff, if it has two charges would be...
Bull Strength 40 x 8 x 2 x 2 = 640gp / 2 (for 2 charge to cast) = 320gp
Bless 30 x 8 x 1 x 2 = 480gp
CLW 20 x 8 x 1 x 2 = 320gp
Total cost would be 320 + 480 +320 = 1120gp, this is affordable in my campaign scale, with abilities that are in line with the campaign items. It should be noted that Spell cast from this staff will be at fifth level , or the casters level, which ever is LOWER.
It should also be noted that house rules have tweaked staves a little. Staves usually allow the casting of 'touch attacks' with a successful melee attack by the stave.
This has been tweaked by the inclusion of staff like wands. They allow 'touch attacks' to be made with a successful 'short' ranged touch attack by the wand (25' + 5'/2 levels, max +10'). They are also easier to carry and conceal, but it should be noted that they are more FRAGILE, and likely to break or snap.
Rods exist, as a means of providing meta magic feat support.
I've already mentioned the inclusion of Mana Potions, which are the spell casters version of Healing Potions allowing the recovery of a first level spell that has been expended from a standard potion.
Scrolls are replaced by 'Tomes' which are books used to scribe scrolls into, who's pages blank allowing the scribing of new spells into it.
Other magic items are in existence, and experimented with, like items that grant some access to feats (like shadow step?), Keystones (intelligent items), and I-Books (like a magical I Pad). 'Stuff' I tweak the rules, play with them, but i make an effort not to break them.
Any ways ... Most of these rules have been tested and ruggedly played with through the twilight campaign, so i'm pretty confident in their game balance (min/max power gamers should be aware there are limitations in place but i'm not going to go into them since this is alot of typing already.)