Got this from one of the best Toyota parts guys in the country.

"Toyota has not published any kind of information that I am aware of that states what the difference in the fluids is. They should not be mixed. They do say" "WS FLUID IS A WORLD STANDARD(WS) FLUID THAT IS NOT INTERCHANGABLE WITH ANY OTHER FLUID AND AT THIS TIME THERE IS NO EQUIVALENT FLUID. DUE TO REDUCED VISCOSITY, IF A VEHICLE CALLING FOR WS FLUID IS FILLED WITH ANYTHING ELSE, THE VEHICLE MIGHT NOT START OFF AT EXTREMELY LOW TEMPREATURES UNTIL THE FLUID IS WARMED UP. THE VEHICLE MIGHT ALSO EXIBIT UNFAVORABLE SHIFT CHARACTERISTICS."

Toyota supplied T4 (what I stock) lists for $4.15 a quart. WS is packaged in a 4 liter steel (like a Coleman white gas can) can and lists for $40.59 ($9.60 a quart according to my high school math )