A few points:
- The standard Mass stipend is set by the local Ordinary.
- Usually (but not in every diocese) a weekday Mass stipend is just the priest’s stipend whereas a Sunday Mass stipend contains the priest’s stipend and a “music fee.”
- While a priest can only keep one stipend per day (visiting priest fees excluded), stipends are still paid for other Masses with the money donated to whatever has been indicated by the local Ordinary (usually the priest’s parish).
- If a parish promises to say a Mass at a specific time and place then it must honor it (extenuating circumstances excluded).
Now, in the case presented perhaps the parish is having difficulty with finances so it is trying to meet its music costs by shuffling Masses around with a priority given to those intentions that have paid the music fee. This “solution” should
not be done since it gives the appearance of trafficking in the sacraments and canon law (c. 947) states that that is to be avoided at all costs (no pun intended).
However, with all of that said, one should also pay the suggested Mass offering unless there is a real financial hardship. Priests should never exclude a Mass intention based on how much is given. But people should also not short the Mass stipend unless there’s actual hardship or difficulty.
What may have happened is that, given the large number of Masses requested, the parish decided it didn’t qualify in their opinion as a hardship case. After all, you were still able to contribute $100 which is no small amount. So the parish decided to simply fit the Masses in where they could.
I’m not saying that’s the right thing to do, but it might be the way they viewed it.