MiniGM is a little off. The cost of a +3 on a weapon is 18000, so the total is 36660. A breakdown of process and source listing follows...
First, determine weapon and cost.
Axe, Orc Double :: 60 GP (Core Rulebook, Equipment)
Need to raise the weapon to Masterwork quality to magically enhance. This process is done during crafting (so before you buy) or by the spell Masterwork Transformation. Either way, increase the cost.
Masterwork, 2 heads :: 600 GP (By RAW, you have to upgrade both heads to masterwork at the same time) (Core Rulebook, Equipment)
Next, make the weapon magic. This is done on a per weapon basis, so you can make one or both heads wounding, or, if you prefer, put different enhancements on the different heads. (Note, this tends to increase bookkeeping, as you have to declare which magic is your primary side, and which is the secondary)
You have to add a +1 enhancement bonus to the weapon first.
+1 magic, 2 heads :: 2000x2 = 4000 (Core Rulebook, Magic Items, Weapons)
Next, add the additional upgrades. To do this, add the enhancement bonus (the + number) to the base price modifiers of your chosen additional abilities. This number leads to an equivalent magic bonus on the weapon, which you then look up on Table:Weapons, located in the Magic Items Section of the Core Rulebook, under the Weapons tab. You then pay the difference between the old equivalent bonus and the new equivalent bonus. For your case
Wounding, +2 each, 2 heads.
This adds with the original enhancement to an equivalent +3, 2 heads :: 18000x2 = 36000. (Core Rulebook, Magic Items, Weapons)
If you were starting with a +1 on both heads, you would subtract the cost of the initial magic (to a total of 32000) however, as you are starting from scratch, you pay for both enhancements. (Ultimate Campaign, Campaign Systems, Magic Item Creation, Upgrading)
To summarize
Base Weapon :: 60
Masterwork :: 600
Magic :: 36000
Total :: 36660
Does the weapon maintain the +3 to hit and on damage or does making it magic take up it bounces.
