Lacto Ice is one of the three standard quality definitions of "Ice cream" in Japan.
The three types are ice cream, Ice milk and Lacto ice.
Ice cream should contain at least 15% of milk solid including more than 8% of milk fat. Ice milk must contact at least 10% of milk solid including more than 3% of milk fat. Then, lacto ice should contain at least 3% of milk solid but does not have to contain any milk fat. By the way, US definition for ice cream is containing milk fat greater than 10%.
Of course ice cream is expensive than ice milk and ice milk is expensive than lacto ice. Usually "ice creams" sold at convenience stores and supermarkets in Japan are most likely lacto ice or ice milk. However, these qualities are higher than you expect.