As ever, I wouldn't let them know the number of hours or price per hour.
"It's gonna cost this much, every week."
They'll either like it or lump it.
Our rate (that we use to price jobs) doesn't differ from commercial to domestic. We think "that'll take 3 hours per week", apply our hourly rate accordingly, multiply it up and then present the overall weekly/monthly figure to the client.
Obviously, the rate we use for this calculation is based on time, materials, staff, profit, etc .. . all rolled into one. Then, as you get slick, it takes less time, but the cost remains constant, thereby increasing your hourly rate (if you want to think of it that way).
Works for us anyway.