Magical weapon enhancemens

[Renen]

Can someone clear this up: to put a magical property on weapon (or armor) does it need to be just masterwork? Or masterwork and +1? Or does masterwork already count as +1?
Say, adamantine weapon, its gonna cos 30xx gold. Can I already put magical properties on it, or do I need to pay 2000 more to make it +1? How would that work?

[BRC]

Weapons must be +1 before any other enhancement may be added.
Weapons must be masterwork to get a +1 bonus.
The +1 Bonus overrides the Masterwork one, giving a +1 to both Attack and Damage (Masterwork only gives bonus to attack)

[Renen]

So say I have a adamantine scythe. It costs 3,018 gp (being masterwork).
I pay +2000 gold to make it +1, and then because I want to add a property on it with a cost of +2, I pay 16k more.
Total cost: 21k correct?

[BRC]

So say I have a adamantine scythe. It costs 3,018 gp (being masterwork).
I pay +2000 gold to make it +1, and then because I want to add a property on it with a cost of +2, I pay 16k more.
Total cost: 21k correct?
Yeah, that sounds right.