It's especially cheap in large tins imported from low-wage countries.
Are you really talking about tomato paste? Tomato sauce and tomato paste are very different.
Yes, I was talking about
large cans of tomato paste, specifically. Here in Europe, a large can of tomato paste from Eastern Europe or the Middle East can be quite cheap
per volume.
Over here it is also available in small tubes and those are not nearly as cheap.
Paste is what can be frozen and scooped portions from: it is thicker and much harder than ice cream, but it's doable with a fork.
Crushed or pureed tomatoes are also cheap but its too watery and would freeze into solid blocks of ice.