I personally run Castrol Syntec 0W-30 in my '07 Phazer.
Be a little careful with the Mobil-1 oil. I'm not 100% sure, but I believe the starter motor utilizes a one-way bearing that is bathed in the engine oil. I've heard that the "Energy-Conserving" oils can cause the bearing to slip, and cause starting issues. The Castrol Syntec is non-energy conserving. Whether or not that claim has any merit, I don't know, but the Castrol is just a few shelves away from the Mobil-1, so it's not like I'm going out of my way to calm my worry.
If the Yamalube stuff was priced competitively, I'd probably stick with that, just because my dealer treats me well. But like you said, a $13 quart of synthetic blend oil is not competitively priced, and as long as the aftermarket oil meets the same specifications as described in the owners manual, it cannot void your warranty.