No official rate is verified. Use a player-entered upgrade comparison checklist and missing-data state, plus a player-observed upgrade checklist and source promotion rule: record personal cash observations, compare cost/effect/goal fields, use the calculator, and avoid claiming an official rate or best method.
Start here when this is the exact player task you searched for. The sections below turn the question into steps, checks, and next pages.
For My Toll Farm money, use the quick answer first, then check whether the topic affects a code reward, event, item, unit, map, build, value, or upgrade path.