Keep in mind the premium fuel sold for cars has massive road tax included, AVGAS does not.
I was speaking to some Shell guys recently at YPAD and YPPF and they were of the opinion that Avgas should be around the same price, but no more than 10% dearer than 98PULP. One thing they specifically mentioned in coming to this conclusion was the lack of the fuel excise on Avgas.
I also mentoined the price we're being asked to pay out in the country to a petroleum distributor I took for a run last Sunday and he figured it shouldn't be more than 10 cents per litre difference than what you pay for it down in the big smoke.
I reckon that 30 cents per litre more is a little over the top.