John L. Sorenson discusses measurements in pre-classical Mesoamerica; argues that Alma 11 is not speaking of coins or weights, but instead a system of measurements in which volume was counted.
John L. Sorenson, Mormon's Codex: An Ancient American Book (Salt Lake City: Deseret Book; Provo, UT: Neal A. Maxwell Institute, 2013), 442-43
Measurement
In the Aztec marketplace, Cortez and his soldiers noted that goods were sold by volumes. In highland Guatemala until around World War I, when scales and weights came into use, market sales were also by volume. Among the historical Quiché, “particular substances were counted by the contains in which they are typically carried.” Popenoe de Hatch reported that archaeological excavation at Kaminaljuyu has revealed sets of ceramic vessels “manufactured to a standard pattern and of graduated sizes that possibly represented established measures for good/grains.”
The Nephites utilized a system of measurement in which volume, not weight, was counted (no scales or weights are ever mentioned). The phrasing of Alma 11:4, 7, and 15 is coordinate with this system in referring to values of “money” in terms of “a measure” of grain (“for a measure of barley, and also for a measure of every kind of grain,” v. 7).