I also can't speak to the actual prices, but to add on to the "workshop" concept sammer is talking about here, a couple months ago Noah Charney was interviewed by NPR on his new book The Art of the Forgery and touched upon this issue.

Like sammer said, works by great artists with workshops were often a "mixture," with pupils painting some things like backgrounds, but the "master" handling more difficult elements like faces, eyes, and hands.

Something interesting he noted was that the masters may have gotten more involved or even handled the whole portrait / painting themselves depending on the price paid. In relevant part from the interview linked above, he states:

We tend to think of artists as individuals creating the work of art in their entirety and that is not the way it has been for many centuries. That's a very romantic notion of how art is created. ... All of the great old masters ran art studios and depending on how much you paid them, they would create themselves a relevant proportion of the work of art.

If you want a Rubens, for example, you pay him the maximum amount then he paints everything himself and he designs it, too. You pay him the minimum, it's still called a Rubens, but he supervises and designs the object, but it might be entirely painted by his pupils and, in practice, it's usually a mixture. Faces, eyes and hands are almost always done by the master because they're the more difficult (if you're talking about portraits). But backgrounds, architectural elements, still lifes — those were almost never painted by the master. And yet anything coming out of the master studio is considered the work of Rubens.

Can't speak to prices but it would definitely have been for upper class folks in terms of affordability. But in regards to who did the actual paintings most masters had apprentices who would start off making the paints and supplies and then eventually would learn do larger parts of the paintings. The master would handle composition and fine details like hands and faces. As time progressed master painters had large workshops to pump out paintings and prints in order to meet demand. Rembrandt is known to have had a rather large workshop and sometimes historians have a hard time telling if he or an apprentice were the one to actually create the painting.

To add upon the price thing, it is nearly impossible to measure costs like that in dollars and cents. Historical economies were differently from modern economies, so even if you said something like "30 1 oz gold coins" and then calculated how much that would be worth now, the buying power of that would likely be vastly different. It would make more sense to discuss in terms of what one could have bought instead of dollars and cents.