Found half a dozen Toyota parts departments that offer 15-25% off the sky-high $15.66 MSRP/quart price.

But they all end up not taking an order unless you pickup; they won't ship liquids (even though from what I can find from a 2016 msds sheet wise the fluid isn't considered hazardous).

Of course the 2 local dealers don't bother with trying to sell parts online. So they are full MSRP - and the one has the gall to even charge above that.

Amazon looks full of sketchy places; have no idea what's actually in the quart bottles you're getting.

Any other tips apart from paying full retail?

I have used amazon but I look'at the vendor selling it and the shipment from USA.

Were the dealers you found on parts.toyota.com? If not, check there.

Wow, learned something new. Checked RockAuto expecting nothing and discovered that there’s aftermarket WS from Beck Arnley for $6/qt.
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Premium Type WS
Beck/Arnley parts meet foreign nameplate OE specifications for form, fit and function. Their product specialists work with a network of global sourcing partners so you can install the right part with confidence.

Features & Benefits:
A superior quality formulation of high-performance base oils and carefully selected additives chemically balanced to protect seals and o-rings
Specifically designed for use in Lexus, Scion and Toyota engines
Formulated using the same technology that OEMs use.
==

I think they mean transmissions, not engines, but it’s clearly ATF.

On RockAuto they sell the brand AISIN WS fluid. AISIN is owned by Toyota and makes a vast majority of the parts on your car. More importantly they design and manufacture the transmission. It is perfectly safe to use that fluid to say the least.
My 2008 with 318K has had nothing but AISIN fluid used in it and it is as smooth as day one.

More Information for AISIN ATF0WS

You don’t change the transmission fluid until 60,000 miles. Why not just buy the good ole OEM fluid and be sure it’s the right stuff.

This!!
How many times will this procedure get done. If you're super lucky, 10. And for others it might be once. But in all likelihood, it will be 3-5. Take your lumps on the OEM fluid and sleep well at night.

+1. I spent a long time looking to save a few bucks on WS until I realized I'll do this every 5 years or so? Saving $20 isn't worth spending so much time looking for fluid... there are better things to do with that time!

So, this will be argued and piss people off.

When I was back home working for a Toyota dealer as a tech, we had Valvoline MAX-LIFE ATF in the pump. If it was not a warranty job (like a warranty transmission/transaxle replacement), that's what it got. It didn't matter if the car had 30,000 miles or 300,000 miles. We had ZERO issues with it. From the cars, trucks, Type-IV vehicles, Hybrids, they all got it. It mixed well with the Dex, T-IV, and WS vehicles if needed, as well.

OEM fluid is good, but this stuff is just as good in my eyes for our application.

Do what you will with this information.