For extrusion adding an inner hole in pasta will make the machine much more complicated. So a tube pasta should cost more than spaghetti.
Adding additional step after extrusion should also increase the cost, so a butterfly pasta (farfalle) should cost more than spaghetti. Because of the bend a butterfly pasta pieces have.
Short pieces of irregular length should be cheaper than long pieces of precise length, because their cutting is easier to do, just continuous process and one rotating knife after the extruder with many holes. So a screw pasta (fusilli) should cost even less than spaghetti.
Pasta is cheaper if extrusion Is possible in a small diameter, to not to make a large machine. Lasagna requires large diameter.
Lasagna scores 2 out 4 expensive characteristics that I can think of. Large size and precise cut. It doesnt have holes and doesnt have bends. So it should not be that expensive.
But if you try to compare other pasta types with this list, their cost isnt dependent on it. Pasta machines are complex, but they are paid off by the scale of production.
And here is the main point, I have no idea how to cook lasagna. I can and do cook lots of other types of pasta that are simpler, and I think this affects the cost the most - popularity. And simplicity of use. If you can sell lots of pasta, you can spend more money to build more efficient machine, for whatever type of pasta that sells the best.