Royal lovers and other favorites were absolutely granted privileges like lands, and depending on the period, would either have ladies-in-waiting and maids from the court itself or would hire them. (The distinction in "lady-in-waiting" and "employee" can be a little nebulous, since even if they weren't paid regular wages, many of them would receive royal wardrobe castoffs, gifts of fabric, pin money, jewelry, and so on, all of which are, of course, functionally pay.)

Anne Boleyn, Henry VIII's favorite who became his mistress and his second wife, was granted the title of Marquess of Pembroke and its attendant lands. This wasn't his first experience pensioning off a woman — the mother of his illegitimate child Henry FitzRoy, Elizabeth Blount, certainly benefited by her son holding a duchy.

In the same period, we have Diane de Poitiers, the maîtresse-en-titre to Henri II of the Valois. Her holdings were notable enough that Catherine de' Medici, Henri's wife, swapped properties with her upon her husband's death, exchanging Catherine's Château de Chaumont for Diane's Château de Chenonceau.

Much later, we would see many intrigues with Charles II of England, who threaded through at least a half-dozen mistresses by which he had children, including the notorious and beloved "Protestant whore" Nell Gwyn.

One of the difficulties with tracing how a royal mistress is paid off is that many of them are career courtiers who are married already. In part, this is because it allows the children of the monarch to lack certainty in their paternity and make any claims to the throne less likely (for instance, Mary Boleyn's — yes, Anne's sister — daughter Catherine was likely sired by Henry VIII, but her name was legally Catherine Carey, and she was never acknowledged as an adulterine bastard), and in part it is because courtiers get paid for their services anyway — who is to say that a particular grant is specifically given in exchange for being cuckolded?

Going to court was always a wildly expensive proposition — the cost of appropriate clothing, the multiple languages requiring tutoring, the education in athletic pursuits like hunting (which required maintaining a horse), and so on and so forth. As a result, families chose to be represented at court by their most educated, clever, and useful relatives, to spend a great deal of time being useful to a monarch in any number of ways, which in turn would translate to patronage opportunities.

If you think of it in U.S. terms, even though your government representatives are in fact paid a relatively modest salary from the U.S. Treasury — quite adequate, but far from lavish — they have a ridiculous number of perquisites, like "fact-finding missions" where they may actually locate a fact, but not on purpose, or lobbyists donating to their re-election campaign funds or to their favored charities, all in exchange for being able to talk directly to them and get favors.

In an era when all privileges flowed from the monarch, it was in the best interest of the nobility to gain his friendship, whether that be by serving as a clever diplomat, commanding his armies, socializing at court with him, or yes, putting your daughter or wife in his bed. In exchange, you would hope to have better luck with your petitions, permission for marriages, grants of lands that had once belonged to your family or were without heirs, etc. etc.