The CannabisDealsUS Cannabis Price Index is a weekly retail price index constructed from online listings across licensed U.S. cannabis retailers. This methodology paper documents the data collection framework, cleaning procedures, taxonomy normalization rules, baseline construction, index formula, coverage scope, governance principles, and known limitations. The index tracks relative price movement across CBD, THC, Vaporizers, Headshop, Grow, and Mushrooms segments using full weekly product snapshots and a fixed baseline structure to ensure longitudinal comparability. Across weekly snapshots, typically only 2–4% of SKUs are discounted in any given week. The average discount depth on discounted products ranges approximately 30–55%. When averaged across all products, this produces a persistent market-level effective discount of roughly 1–3% per week. Associated dataset (concept DOI): https://doi.org/10.5281/zenodo.18351089 This document serves as the citable methodological reference for the CannabisDealsUS Cannabis Price Index.