Yea, allow about 6 to 10 yards of concrete for starters.
Not sure how big of a hole that would take right off in dimensions.

That's in the ballpark of a small concrete house foundation, isn't it?

That would be 162 cu ft (for 6 yards of concrete) or
10 x 10 x 1.6 ft, or
6 x 6 x 4.5 ft.

For reference, 10 yards is the typical capacity of a cement mixer
truck.

For any project, you need to look at the total cost of installation
and all components, not just the primary component.

As you have shown there are many ways to pour the material . I am sure the
tower maker has their recommendations. I doubt it would do much good to
have it only 1.5 feet deep and 10 feet wide. I would think it would be
poured in more of a cubic form but deeper than it is wide. Also there is
all the rebar to install correctly and if it is like some Rohn tower there
is a specification of some rocks and sand at the bottom of the hole.
Towers are not somthing youjust stick up and hope for the best.