Buy the coolant from them, and give all your other maintenance money to
someone else. If you use a different coolant, they could use that as a
(possibly lame) reason why something failed under the hood.

I also have a V-6 '99 Tacoma 4X4 extra cab that I purchased last year
with 75K on the odometer. I had the transmission flushed and after a
talk with the local Toyota service manager put Peak Long Life
anti-freeze in it.( http://www.peakantifreeze.com/aboutus.html )He said
that they were not demanding that Toyotas propietary anti-freeze be used
anymore.

Of course, mine is not a certified truck and I don't have to satisfy
anyone but me.

--
Jarhead