I never expected this thread to be revived 2 years later and become controversial. I'm the original poster, and I never did buy a Prius. Just by chance shortly after I posted this thread, a friend of mine offered me his 2006 Caravan for a very cheap price. That's what I bought for my milk transporting vehicle. The Caravan is a 4 cylinder, and it usually gets between the low 20's and 30 mpg. My wife loves minivans, and she's the driver for milk delvieries, and the Caravan just worked out perfectly, we just took the back seat out to make room for the transport tanks. It's a little underpowered when it's loaded with milk, especially in the mountains in upstate New York and Vermont where we're located but it's worked out well for us.
As for the Prius, our sheep shearer drives a Prius. He shears sheep all over upstate New York and Vermont, and he swears by the Prius. He carries all of his shearing equipment of course it's no where nears as heavy as milk, but he does carry a lot of equipment. He puts a huge amount of miles on it, and he's never had any problems with it in 2 years. He says he'll definitely get another.