Public GPU price catalog

PUBLIC, no authentication, read-only. Every GPU machine sold online at a public price, in the versioned price feed schema (same data as https://gpucloud.ca/feeds/gpu-prices.json, the CSV and RSS feeds and https://gpucloud.ca/llms.txt): prices in CAD, taxes extra, dated by catalogDate. available and availabilityUpdatedAt are present only when read from a fresh stock snapshot (less than 2 minutes old), otherwise omitted. Cached 15 seconds (Cache-Control: max-age=15). Rate limited to 60 requests per minute per IP (429 with Retry-After). CORS open for GET.