Do the price displays not show the unit price or per kilo price, it makes it much easier to see which is cheaper, if not bring a calculator.
The unit price is normally a useful guide, but with ice cream a per-litre price can be misleading. Some brands have a lot of air whipped into the mix. Some of the premium brands are far more dense, packing a lot more ice cream into a smaller volume. This can be better value - provided, of course, that you eat it with a small spoon so as to savour the densely packed flavour in every mouthful......
On the other hand, the 'half air' brands do have the advantage that when you take them from the deep freeze, it is a little easier to pry loose a scoop; With a more dense ice cream, it is easier to leave it out of the freezer for 10 minutes before serving - which is not ideal unless you are serving up the entire tub. So if you are inclined to buy a tub and make it last a couple of weeks, heavily aerated ice cream is the product for you.
What you really need in the Supermarket is a portable scales so that you can weigh the ice cream. Or you can run over the fruit and veg section with the different brands to satisfy yourself as to which contains more by weight.
Of course, this is only part of the battle. If you like a nice rasberry or black cherry ice cream, the relative density of the fruit ingredients can have a significant bearing on the value of the product.
Really, it's a constant struggle to conquer the notorious problems inherent in securing good value in ice cream.