Ah, no. This is one of those “could they not afford a thesaurus?” moments, where they keep using the same word for slightly different things.
There is a difference between an enhancement bonus to some particular roll, and an enhancement bonus to the weapon itself, which is a property that items can have. They re-use the name because enhancement bonuses to items usually result in those items giving enhancement bonuses to certain things, but it’s still pretty unclear.
Being a masterwork weapon adds a +1 enhancement bonus to attack rolls. Having a +1 enhancement bonus to a weapon also adds a +1 enhancement bonus to attack rolls, as well as a +1 enhancement bonus to damage, but it is also more than that. For example, having a +1 enhancement bonus to the weapon also improves its hit points and hardness, allows it overcome DR /magic, and makes it eligible to receive special weapon properties. Having a weapon that offers enhancement bonuses on some or all rolls relevant to that weapon’s use is not the same as having an enhancement bonus to the weapon.
Since a +1 weapon is always also a masterwork weapon, it has two separate +1 enhancement bonuses to attack rolls, and these don’t stack.
And when the rules say that a magic weapon must have a +1 enhancement bonus before you can add special properties, it means that it must be a +1 weapon, not merely that it must have enhancement bonuses to the right rolls. So even if you found some other way to add a +1 enhancement bonus to the weapon’s damage, and also had a +1 enhancement bonus to attack because it’s masterwork, that still wouldn’t quite qualify.
That means your +1 benevolent rapier needs to be a rapier (20 gp), that is masterwork (+300 gp), that has a +1 enhancement bonus (+2,000 gp), and then has the benevolent property (+6,000 gp for going from +1-equivalent to +2-equivalent). Total cost is 8,320 gp. With 2,320 gp, you can only afford a +1 rapier.
In neat tabular form:
Item or enhancement |
Cost |
rapier |
20 gp |
masterwork |
300 gp |
+1 enhancement |
2,000 gp |
benevolent property |
6,000 gp |
Total |
8,320 gp |
In this case, the order they’re written is also the order in which these have to be applied: each line is a requirement for the next one.