Do I have to use yamalube? Where is the best place to purchase oil?

2006 Yamaha 175hp vmax (hpdi)
Separate gas and oil tanks.

Pat Goff can tell you the peril of running cheap oil in your motor. I would run Yamalube & Ring Free.
Check out domo-line.com Even with paying cheaper it's going to be cheaper than buying it retail. The dealerships are a rip-off.

As an example I run Evinrude XD-100 and get it for $34.50 delivered to my door.

You absolutely do not have to use Yamalube in that engine. Pennzoil and Quicksilver burn much cleaner. Many many people are using those two in their Yamahas and have for years, myself included...and many complain about the carbon and fouled plugs with Yamalube.(do some Google searches) Pennzoil is $18 at Academy. I have no idea why people assume cheaper priced oil equates to bad oil. Higher prices are usually attributed to things other than quality.

Have a 2001 Yamaha V-Max bought it used. Owner was running Yamaha lube and I still run Yamaha and ring free in every fill up. So far no problems still running strong. May cost me more in the long run but piece of mind is a lot. Kinda like the confidence bait.

Some Yamaha dealers, both outboard and motorcycle have Yamalube 2M in bulk.
Some have their own containers others bring your own. I'm buying mine for $29 from dealer
in his containers.

I've been running Quicksilver premium plus for the last ten or so years in my HPDI and it burns cleaner than the yamalube.