My city charges $300 just to pull a permit, and an electrician charges $100 just to show up. Then at minimum you'll need a new branch circuit, breaker, conduit, fittings, outdoor box, wire, interlock kit, and the outlet. And you better hope your breaker box has availability for a new branch and that it's recent enough for an interlock kit. If not, you'll need to replace the entire panel and all circuit breakers. And in my jurisdiction, grounding requirements had recently changed, and my local inspector required that I bring the grounding up to code in order to have any work approved.