This is a difficult question to answer, but my reaction is often neither project or hour based.
I tend to see the world of consulting (AI or otherwise) through the lens of value; a measure of economic benefit the solution provides. Sometimes the economic benefit is time saved. Other times, it could be compressed time-to-market. And yet, another could be the opportunity losses deflected by avoiding distractions.
The hard part in almost every case is determining value. And to be clear, there’s one more layer - you can’t ask for the total value of the solution; your price must be discounted from the total value to compel buyers to “partner” with you to reap the benefits. Indeed, the free market forces suggest you best leave money on the table.
These are really good vectors, but they are each meaningless until you add some value metrics. What will these approaches achieve for the buyer of your services?
Lastly - the cost (not to be confused with your price) is the measure you will compare with your value-based price to determine if it is profitable.
Ironically, let’s use an ice maker as an example. 
After all, it was the first robot-like AI tool to enter the home in 1953, the year I was born.
John Gorrie, and the first commercially available ice maker was created by Thaddeus Lowe in 1866. But neither of these machines let owners make ice at home. It wasn’t until 1953 , when Servel began selling refrigerators with built-in ice makers, that ice could be made at home without having to use an ice tray.
- The ice maker has a clear economic advantage to consumers; it makes, cubes, and dispenses ice automatically. And it repeats this process intelligently.
- It eliminates the drudgery of filling trays, popping ice cubes out of trays, and generally distracting you from other matters in life.
- This value is pretty easy to calculate if you know how much each consumer values an endless supply of ice without distractions. Apparently the cost of making ice makers is well below the value they serve since to this day, every refrigerator has one.