I would want to actually be certain toyota is talking about a valve adjustment as well, cylinder head shops don't even offer a price that good and in my experience I've personally had a Toyota dealership tell me the valve cover gaskets alone are an $800 job (which I laughed in their face for, of course)
On one hand if they insist they would be replacing shims, $800 would be highway robbery and it would be hard to pass up. But also alluding that they would re-use gaskets is a pretty big red flag too... if anything I would be a hesitant they would upcharge at the very end, like Tim said it's a price almost too good to be true. I work on cylinder heads myself, and in the past our sales department has offered some pretty ridiculous pricing because they're oblivious to the work that goes into the services they sell
I would do some more digging on them, personally