The only question that needs to be asked, imo, is whether or not the Dextron meets the Toyota criteria. If it doesn't, then I wouldn't put it in my transmission, no matter what the savings. While I have no doubt that a 30000 mile run in isn't going to ruin your transmission, I wonder what the long term results are. What is the replacement cost of a Toyota/Lexus transmission. Vehicle manufacturers, auto, truck, bus, even airplane, specify lubricants that meet their engineering specifications. There has to be a reason that Toyota specified the Type IV.
I think you are in a minefield - you might make it out ok, you might not! :)