This is using a Two-Bladed sword as a weapon with both ends being masterwork though only one enchanted… Basically it’s the most expensive there is.
Incorrect! If you're only enchanting one head, a double-headed weapon costs no more than an ordinary weapon. Now, a Cold Iron weapon... *Shudders*
+1 = 108xp and 1350gp
+2 = 348xp and 4350gp
+3 = 748xp and 9350gp
+4 = 1,308xp and 16,350gp
+5 = 2,028xp and 25,350gp
+6 = 2,908xp and 36,350gp
+7 = 3,948xp and 49,350gp
+8 = 5,148xp and 64,350gp
+9 = 6,508xp and 81,350gp
+10 = 8,028xp and 100,350gp
...How are you getting these numbers?
The base price for a +1 bonus is 2000. To enchant a magic item, you use half the base price in GP (more if Cold Iron, less if certain synergies or item templates, varying based on some other factors) and 1/25th the base price in experience. The table would go like this, assuming no Cold Iron, synergies/templates, etc:
+1 = 80xp and 1000gp
+2 = 320xp and 4000gp
+3 = 720xp and 9000gp
+4 = 1,280xp and 16,000gp
+5 = 2,028xp and 25,000gp
+6 = 2,880xp and 36,000gp
+7 = 3,920xp and 49,000gp
+8 = 5,120xp and 64,000gp
+9 = 6,480xp and 81,000gp
+10 = 8,000xp and 100,000gp
So… That seems odd really… A +10 = 200,000 in price but a +5 Enchantment bonus is 50,000 so… Wouldn’t a +5 Enchantment and a +5 Special Ability be 100,000? The DMG says it’s 200,000 though… Seems a bit odd to me.
No, because the enhancement bonus and any special ability priced equal to enhancement bonus are added together to determine the base price of the weapon, as the table explains.
Now, there are also special abilities given flat prices, as opposed to priced in bonus equivalents, and those work a little differently.