Is that what the Calvinists have been telling you?

It depends on time period. Indulgences weren't things that were for sale before the High Middle Ages, and then their sale was controversial. It was part of the motivation of the Protestant movement, and much curtailed during the Catholic Counter-reformation.

And then there absolutely were some (many, maybe) nobles and merchants who were genuinely devout. Even emperors, like Louis the Pious. I'd imagine they tried a little harder.

I mean... there is no 'one thing' any Catholic has done. There have been faithful Catholic Lords/Monarchs, and there have been not-so-faithful ones. Making blanket statements like 'actual fasting was pretty much a poor people thing' is not really a good description. Fasting is really something only the rich can do anyway, since if you're already poor... you're not missing much. There have been very faithful Catholic noble families (the Habsburgs come to mind -- many are still quite faithful today!) and they certainly did the normal fasting.

That being said, I've never heard of replacing the fasting days with a 'repentance fee'. I'm not going to say it's never happened because there have been billions of Catholics, and probably millions of priests so maybe someone did that somewhere. However, under normal Catholic doctrine it's impossible to pay to repent. God's mercy is freely given without money.

From Poe Assistant:

In the Catholic Church, both indulgences and penance are related to the forgiveness of sins, but they have different functions and purposes.

Penance is a sacrament in which a Catholic confesses their sins to a priest and receives absolution for them. The penitent is then required to perform some act of penance, such as prayer, fasting, or almsgiving, as a way of expressing sorrow for their sins and making amends for them. The purpose of penance is to reconcile the penitent with God and the Church and to help them grow in holiness.

An indulgence, on the other hand, is a remission of the temporal punishment due to sin, which is a consequence of sin even after it has been forgiven. The Catholic Church teaches that sin not only offends God but also disrupts the order of the universe, and therefore, it requires satisfaction or reparation. Indulgences can be granted for specific acts of piety, such as visiting a holy site or performing a particular prayer, or for performing certain charitable works. The purpose of indulgences is to reduce or eliminate the temporal punishment due to sin and to facilitate the process of sanctification.

It is worth noting that indulgences have been a controversial topic in Church history, and their use and abuse have been the subject of much debate. In the 16th century, the sale of indulgences by some Church officials became one of the factors that led to the Protestant Reformation. However, the Catholic Church has since reformed its teachings on indulgences, and they are now granted under specific conditions and with a clear understanding of their purpose.

Anyway, that's not how indulgences work. They aren't a matter of "gain this indulgence and I get to indulge in something that's normally a sin."

Since fasting and abstinence are a matter of Church Law and not Divine Law, the practices can be the subject of a dispensation or commutation by an authority such as the pastor. For example, on St. Patrick's Day in these United States, when it falls on a Friday (as it did this year) it's customary for bishops to grant dispensations for the faithful to enjoy corned beef, or a commutation, to pray the Rosary and then enjoy corned beef (or pork tempura).

Whether any given pastor could be influenced by the money from a "rich lord/merchant" is left as an exercise for the reader, but if practically all his parishioners are tithing and paying his salary anyway, then what can you do?