I have a gas furnace Goodman model#capf3030b6ba. I am trying to get an estimate of how much it costs for tax purposes. My contractor paid the subcontractor for the unit and the installation but I never received a receipt or much info about the unit. How much do these units cost?

Depends on who buys and where. Ask the HVAC contractor for a bill. Who paid for this install and how was it paid?