Buy a used Windows 10 Pro laptop from eBay ($80). Wipe it clean with a fresh Windows install.
Install OBD Auto Doctor (Free tier) or Car Scanner ELM OBD2 (Free for iOS/Android). Pair this with a BLE OBD2 dongle ($25). carsoftware 52 free
Purchase a VXDIAG VCX Nano (for specific brands like BMW or Volvo, ~$100) or a Vident iLink400 ($120). These come with legal, limited-time software. Buy a used Windows 10 Pro laptop from eBay ($80)