### Replace "transaction price" terminology with "cost"
"Transaction price" never quite stuck. "Cost" is simpler, shorter, more intuitive, consistent with `--cost` and "cost reporting", and more distinct from "market price".
There is an (acceptable) ambiguity: "cost" could mean the `@ UNITCOST` price attached to the amount, or the total cost when the amount is converted (`QUANTITY * UNITCOST`).
Status: as of 2023Q1 this has been done in the manuals and is slowly ongoing in the code.