The 5w30 you were looking at was probably the xl-7500, which is to be changed every 7500 miles or 6 months. The 0w 30 is a series 2000 oil with longer drain intervals. Hence the difference in price.
I use in my WRX Amsoil 2000 0w/30 or 3000 5w/30 diesel oil. I autocross quite a bit. Never had a problem in 19000 miles. 5w/40 is a bit heavy and not needed...