This itched me everytime I bought a special weapon/armor for a character and wanted to improve it. The hardest time I had with the Sunblade: Its a +2 weapon which is +4 against evil creatures and costs 25.335 gold basically. How much does it cost to improve the enhancement bonus? When I have upgraded the weapon to +3, is it a +5 weapon against evil creatures (giving a +2 special weapon property bonus ) or will it be +4 as written instead?
This itched me everytime I bought a special weapon/armor for a character and wanted to improve it. The hardest time I had with the Sunblade: Its a +2 weapon which is +4 against evil creatures and costs 25.335 gold basically. How much does it cost to improve the enhancement bonus? When I have upgraded the weapon to +3, is it a +5 weapon against evil creatures (giving a +2 special weapon property bonus ) or will it be +4 as written instead?
It's pretty simple, actually.
Just look at the price. It's 50,335. This is the cost of a +5 bastard sword. So, if you want to boost it by a +1 the cost is 72,335 - 50,335 (The cost of a +6 Bastard Sword) = 20,000gp.
It would be a +3 weapon which is either a +5 or +6 against evil creatures, and does double damage against undead or negative plane creatures (those stack, by the way, so it'd be a +5 double damage vs evil undead). It also wields like a short sword.
+2 Weapon
+1 Wield like Short Sword
+2 +2 or double base Bonus vs evil with double damage to undead & negative plane creatures.
+5 total.
Looking at the above... I'd say the +2 doubles the base bonus, and make it a +3/+6 vs Evil with Double Damage for Undead & Negative Plane Creatures. The reason for this is that if it was just a +2 vs evil, that's more like evil bane, but it doesn't do +2d6. The only way to justify it is to say the +1 doubles the base bonus vs Evil. Plus, doubling the base bonus matches with the double damage vs undead and negative plane.