The correct pricing is method 1: Count the most expensive spell before reducing price for multiple-charge cost.
Benchmark: staff of fire
The staff of fire has burning hands (1 charge), fireball (1 charge) and wall of fire (2 charges). It costs 28,500 to buy, or half that, 14,250 to craft.
Before any reductions, on 375 * casterlevel * spell level alone, the most expensive in order are wall of fire (12,000 gp), fireball (9,000 gp) and burning hands (3,000 gp). Placed in that order, the cost is as follows:
- Wall of fire: 12,000 * 0.5 (for costing two charges) = 6,000 gp
- Fireball: 6,000 * 0.75 (for being the second spell) = 6,750 gp
- Burning hands: 3,000 * 0.5 (for being the third spell) = 1,500 gp
- Total: 14,250 gp (the correct craft price!)
If you applied the half-price to the two-charge spell first, it would change the order to make fireball the first spell, giving this incorrect calculation:
- Fireball: 6,000 (first spell) = 6,000 gp
- Wall of fire: 12,000 * 0.75 * 0.5 (for costing two charges and being the second spell) = 4,500 gp
- Burning hands: 3,000 * 0.5 (for being the third spell) = 1,500 gp
- Total: 12,000 gp (the wrong craft price!)
Therefore, the correct calculation must be to calculate the most expensive spell before applying the discount for multiple charges.
According to the text, you then apply any discount for charge cost, but note that rules-as-written, it doesn't say anywhere that you can make more than a two-charge cost, even though some items are found with a five-charge cost. Ten charges may be pushing it.
Then, only having determined the price in this manner can you begin crafting, whereupon you spend the material components.
Final price: 51,735 gp and 37.5 cp
All spells must be at the same level, and the minimum caster level on heal is 11. Hence our prices before spell components are:
- Heal: 24,750 gp * 0.5 (two charges) = 12,375 gp
- Raise dead: 20,625 gp * 0.75 (second spell) * 0.1 (ten charges) = 1,546 gp 87.5 cp
- Restoration: 16,500 gp * 0.5 ( third spell ) * 0.5 (two charges) = 4,125 gp
- Cure serious wounds: 12,375 gp * 0.5 (fourth spell) = 6,187 gp 50 cp
- Subtotal: 24,234gp 37.5 cp
Next you must pay spell components equivalent to casting the spell the maximum number of times the staff can, accounting for charges: 25 * 100gp for restoration, and 5 * 5,000 gp for raise dead, total 27,500 (more expensive than the spells themselves!)
The total craft price of your staff is therefore 51,734gp and 37.5cp.
The Table
I believe the table you're looking for is Table 7-33 Estimating Magic Item Gold Piece Values on PHB 285. The two rows you're interested in are
\begin{array}{l|l|l}
\textbf{Effect} & \textbf{Base Price} & \textbf{Example} \\ \hline
\text{Ability bonus (Enhancement)} & \text{Bonus squared} \times 1000\text{ gp} & \textit{Gloves of Dexterity +2}\\
\text{Skill bonus (competence)} & \text{Bonus squared} \times 100\text{ gp} & \textit{Cloak of elvenkind} \\
\end{array}
I don't believe there is any magic item (in the core rule books, anyway) that directly provides an Enhancement or Enchantment bonus to a skill.
However, all skills are based on an attribute (strength, dexterity, constitution, intelligence, wisdom, or charisma). An Enhancement bonus to that stat (say, a +2 Cloak of Charisma) will provide a boost to skills based on that attribute (for Charisma, say, Diplomacy) as if your attribute were naturally that much higher.
Crafting
If you're interested in crafting these items yourself, check out the PHB's Feats section for feats such as Forge Ring (PHB 94) or Craft Wondrous Item (PHB 92). The cost to create an item is 1/1000 item price in days, 1/25 item price in XP, and 1/2 item price in GP for materials.
There are also special requirements for some items; namely, for the competence bonus items, the creator must have ranks in the skill equal to the bonus the item will grant.
Best Answer
Mechanical Trap Minimum Cost
It doesn't look like you're pricing that trap correctly. Here's from the mechanical trap rules:
And from the trap creation rules:
By the rules, you can't create a trap below CR 1, and the minimum cost is 100g.
Trap Math
Lets look at your costs compared to the rules. The base cost is 1000g.
Correct, this is no change to the base cost.
Correct.
No modification to cost.
Correct, so a search DC of 15 would be a modifier of -500. Total of -700. You have no extra costs, as there's no alchemy involved.
Your cost is calculated as such:
So you have (1000 - 700) x 1 + 0 = 300g. You could get it down to 100g if you lowered the save DC on the pit to 18 instead of the base 20.
Note that you currently have a CR 0 trap, and the rules require minimum CR of 1. You can get to 1 without increasing the cost by adding average damage (adding 7 average damage increases CR by 1). This would not increase the cost.
What if it really didn't have a cost?
If something really doesn't have a cost, you can make something up. For "digging a hole in the ground", the cost is time. The PCs can do it themselves, or they can hire someone. An untrained labourer costs 1sp per day.
The economy in 3.5 doesn't make a ton of sense, so you can assume the extra cost in a trap vs a hole in the ground is what's required to actually fool anybody into ever falling into it. It's best not to try to expect too much logical consistency on this stuff, becuase unless you use houserules, it doesn't exist.
How Long Does Digging a Hole Take?
Races of the Dragon p.98 has rules for using Profession (Miner) to mine, which you could also use for digging a big hole for your trap. The rules cover how long this would take based on how good a check you can make, with modifiers for different type of ground. You could combine those with the hireling cost to get an idea of what it'd cost to hire a bunch of people in town to dig a 10x10x10' hole.
(Summary version: a medium size miner can empty a 5' cube per day with a DC 15 check. DC 10 would do half of that, and every 5 you beat it over 15 lets you do another 5' cube. Large size works twice as fast, small half as fast. A second medium miner can assist and use aid another to boost the role, while smaller creatures can have more assistance.)
Now that you have your hole, you'd just have to figure out how to conceal it. There's no particular rule for that outside of the trap rules that I know of, but you could make something up.