"few days of work" for "tens of thousands of dollars" seems a bit absurd. Are you assuming they are making 10K per day? Seems a bit high. I would assume 200-300/hour tops.
The amount of time you can spend preparing the training data is unbounded. The number of times you can do the training with data that ends up not actually looking like what you see in-the-wild a week later is unbounded. When all is said and done, the yak-shaving alone will be tens of thousands.
At the rate of a couple of hundred bucks an hour that I'd expect to pay for a qualified consultant, 200 hours works out toward the high end of the few in "a few tens of thousands".
How do you cram 200 hours into a few days?
Just like with the vast majority of project forecasts the "few days" is what you say to get the sale - internally or to outside clients. If you think it is that simple, well, I would like to sell you just a few days of machine learning expertise if you have a project... :) Even very simple tasks that you can let the intern do can - and often does - take days longer than projected.