Dianne, you would found it still cheaper going through Switzerland and quicker. The difference in diesel price is 10 cent per litre, assuming you use Austria Euro fuel rate against the swizz franc, but You also using more fuel, at least 4.5 gallons more!going the Austrian way each way, [about 20 litres]or about 20 euro,s, so your saving of 10 cent a litre is actually a minus 18 euro's each way. plus you would need to buy more fuel in Italy which is dearer,pay more tolls in Italy too using the Austrian route, which adds another 20 plus euro's each way.
TWO Austrian vignettes and two Brenner pass tolls, adds up to over 30 euro's, assuming you are using this route both ways and are staying in Italy for more than 10 days.
So that extra cost adds up to 100 euro's approx, and two switz vignettes on the other hand, does not cost anywhere near 100Euro's.
But the Austrian route is prettier.