How would you price before and after listing content at $600 a house?

Two a month means one a month. Assume that with any referral promise and there won't be disappointment.

The thing you're actually selling here isn't the video, it's the before. Any photographer can shoot a finished kitchen. Almost nobody has the framing and the demo footage, because you have to be there in week two to get it. That's a real moat and you should price it like one. I'd say yes at $600 for the first two and tell her plainly it's an introductory number while you learn her clients' timelines.

Scope creep warning, since it's my whole personality. On your own job you shoot when it's convenient. On someone else's, the studs are covered by the time they call you, and then you're doing a second trip, or worse, you're standing around while the painter finishes the trim you need in frame. Write into the quote how many site visits are included and what a re-shoot costs. Otherwise $85 an hour becomes $40 by the third house.

Get the usage terms on paper before the first shoot. Who can post the footage, for how long, and whether the client can hand it to a different agent next year. Also whether the original creator can keep using it on their own page, which is usually the point. These are ordinary contract questions and a one page agreement handles them, but the default when nothing is written is an argument later. On whether producing video for a broker triggers a licensing requirement, that is a state real estate commission matter and the answer varies by state, so the broker should point to their rule and it should be confirmed with someone licensed in that state.

@wendy_park48 is right about the broker piece. Practically the way it works most places is the broker owns the advertising and has to approve it before it runs, so your video is her problem to clear, not yours. That does mean revisions. Build in one round free and charge for the second, because a compliance edit is still an edit.

$600 twice a month is $14,400 a year for maybe 170 hours. That is real money if it is steady and it is noise if it is not. The number worth knowing is whether that agent is the only source. One agent as the entire client base is the same risk as one tenant in a building.

Take it and stop analyzing it. But do one thing first: shoot the next house on the list as though it were a paid job, with the agent's timeline and deliverable spec, and time it honestly. That settles whether seven hours is real or just seven hours because nobody's waiting. @omar_haddad's second trip is where the number goes wrong.