Using the rules from the new Artificer's Handbook by Mystic Eye Games, this is how I would come up with it:
SRD:
Lordly Might
This rod has functions that are spell-like, and it can also be used as a magic weapon of various sorts. It also has several more mundane uses. The rod of lordly might is metal, thicker than other rods, with a flanged ball at one end and six studlike buttons along its length. (Pushing any of the rod’s buttons is equivalent to drawing a weapon.) It weighs 10 pounds.
The following spell-like functions of the rod can each be used once per day:
Hold person upon touch, if the wielder so commands (DC 14). The wielder must choose to use this power and then succeed with a melee touch attack to activate the power. If the attack fails, the effect is lost.
Fear upon all enemies viewing it, if the wielder so desires (10-foot maximum range, DC 16). Invoking this power is a standard action.
Deal 2d4 hit points of damage to an opponent on a successful touch attack and cure the wielder of a like amount of damage (DC 17). The wielder must choose to use this power before attacking, as with hold person.
The following weapon uses of the rod have no limits on their use:
In its normal form, the rod can be used as a +2 light mace.
When button 1 is pushed, the rod becomes a +1 flaming longsword. A blade springs from the ball, with the ball itself becoming the sword’s hilt. The weapon lengthens to an overall length of 4 feet.
When button 2 is pushed, the rod becomes a +4 battleaxe. A wide blade springs forth at the ball, and the whole lengthens to 4 feet.
When button 3 is pushed, the rod becomes a +3 shortspear or longspear. The spear blade springs forth, and the handle can be lengthened up to 12 feet (wielder’s choice), for an overall length of from 6 feet to 15 feet. At its 15-foot length, the rod is suitable for use as a lance.
The following mundane uses of the rod also have no limits on their use:
Climbing pole/ladder. When button 4 is pushed, a spike that can anchor in granite is extruded from the ball, while the other end sprouts three sharp hooks. The rod lengthens to anywhere between 5 and 50 feet in a single round, stopping when button 4 is pushed again. Horizontal bars three inches long fold out from the sides, 1 foot apart, in staggered progression. The rod is firmly held by the spike and hooks and can bear up to 4,000 pounds. The wielder can retract the pole by pushing button 5.
The ladder function can be used to force open doors. The wielder plants the rod’s base 30 feet or less from the portal to be forced and in line with it, then pushes button 4. The force exerted has a +12 Strength bonus.
When button 6 is pushed, the rod indicates magnetic north and gives the wielder a knowledge of his or her approximate depth beneath the surface or height above it.
Caster Level: 19th; Prerequisites: Craft Rod, Craft Magic Arms and Armor, inflict light wounds, bull’s strength, flame blade, hold person, fear; Market Price: 70,000 gp.
First off - damn!
Second off, these are its abilities (in a nutshell):
1/per day each:
hold person (via a touch attack)
fear (to those within viewing range)
2d4 points of damage or healing
use-activated powers (unlimited)
+2 mace (Default)
+1 flaming longsword
+4 battleaxe
+3 spear
Misc:
climbing pole/ladder with a +12 strength modifier
points to magnetic north, and reveals depth.
So, the cost is calculated as follows:
Hold Person -> 5 for use-per, +4 for 1 use per day, -2 range increment decrease from medium range, to touch. Caster level 3, spell level 2.
Fear -> 5 for use-per, +4 for 1 use per day, -1 limitation (only affects creatures who see the effect - nonstandard from Fear spell), -1 decrease in range from 30-ft. to 10-ft, +1 for second effect. Caster level 7, spell level 4.
2d4 Cure/Heal -> 5 for use-per, +4 for 1 use per day, +1 cost for being able to reverse as desired, +2 for third effect. Caster level 1, spell level 1.
Cost formula: 10gp(spell level + caster level -1) * number of spell slots^2
Hold Person = 10gp(2 + 3 - 1)*7^2 = 10(4)*49 = 1,960gp
Fear = 10gp(4 + 7 - 1)*9^2 = 10(10)*81 = 8,100gp
Cure/Heal = 10gp(1 + 1 - 1)*12^2 = 10(1)*144 = 1,440gp
Bonus items:
+2 mace = # of slots 2 + (+2), +3 (4th effect) =7. Spell level = 3 (bonus +1). Caster level = 6 (2 x spell level)
+1 flaming (+1 equiv.) sword = # of slots 2 + (+1 sword) + 2 + (+1 flaming) + 4 (5th effect) = 10. Spell level = 3. Caster level = 6
+4 battleaxe = # of slots 2 + (+4) +5 (6th effect) = 11. Spell level = 5. Caster level = 10
+3 spear = # of slots 2 + (+3) +6 (7th effect) = 11. Spell level = 4. Caster level = 8
Cost formula: 10gp(spell level + caster level -1) * number of spell slots^2
+2 mace = 10gp(3 + 6 - 1)*7^2 = 10(8)*49 = 3,920gp
+1 flaming sword = 10gp(3 + 6 - 1)*10^2 = 10(8)*100 = 8,000gp
+4 battleaxe = 10gp(5 + 10 - 1)*11^2 = 10(14)*121 = 16,940gp
+3 spear = 10gp(4 + 8 - 1)*11^2 = 10(11)*121 = 13,310gp
Total all these costs:
1,960gp + 8,100gp + 1,440gp + 8,000gp + 16,940gp + 13,310gp = 49,750 gold pieces.
Now, that doesn't include the "magnetic north" and "climbing pole" thing. Those abilities are a bit more complicated, and I've already spent a fair amount of time (at work no less) calculating this. However, 49,750gp does seem fair for an item such as this one, minus those last two abilities. The Fear effect is relatively weak, as is the Hold Person effect. So those costs are relatively low. Being able to switch between all those weapons is handy, but not overly so. The final two effects are really just window dressing, and won't make or break your campaign world. I'm not sure they were worth 20,250gp worth to equal the DMG's 70,000gp. In fact, I would price the item somewhere around 60,000gp.
Well, in any case, that's the beauty of our system, yes it's a bit complex because this item is complex, but it does generate a very real, very fact-based number that you can take to the bank.
