Considering I dragged it out over something like 12 years, probably more than necessary at various rates throughout two decades in everything from a college classroom to a couple of instructor's living rooms and also the sitting at the airport after or before a training flight version. Even got grilled by one instructor once while I was grilling dinner for him and another pilot friend who was also working on his instrument rating, on my back porch.
Generally though, the answer you're seeking isn't answerable because you can either be way ahead of the game with self-study, and only need review and confirmation by your instructor, or you can pay to have the instructor spoon-feed you every topic and concept.
Especially with the Instrument rating, you're very in control of your fate in this regard.
Example: Instructor for today's lesson wants to cover the "ILS Approach". If you've never heard of one, you're going to be there for a few hours. If you have read up, they're going to cover the basics and see that you've done your homework and move pretty quickly through it all.
Rates, like I said, everything from paying for college credit hours in a formal ground school to feeding the instructor steak and veggies on my back porch. For the most part, when I studied or reviewed with a CFI-I at an airport they charged their usual hourly rate for instruction but I noticed that the nicer ones rounded down a bit over the very long haul. Some track their time to the minute, some to the quarter hour, some just made up a number that wasn't ever longer than we actually spent. Overall I feel like I got a lot of time for free that I probably shouldn't have and whenever I noticed it, I'd offer to pay for it.
Now that I'm working on becoming an instructor I see no significant reason to not continue these "traditions" others offered to me. If you wanted to invite me to dinner and feed me while we talk airplanes and I toss questions at you, and you're not a jerk, I'll stop by. Dinner is always fun with other pilots. If we're pushing you toward a rating and a checkride and you need the formal sign-off that you know your stuff and a review, we're probably at the airport and on a clock. But I'm not going to spend a lot of energy starting a stop watch when you arrive and making sure to bill you for every single minute if you're progressing and doing your homework. I'm going to look at my watch and if we do a couple of hours you'll pay for a couple of hours. I won't waste your time during those hours either.
That said, I do have a copy of the Toggl app on my phone if you're a "problem child" who isn't putting in the effort, and I know how to print you a detailed invoice. LOL.