Those in heaven or hell have no use of our intercession, as they either have chosen to reject God or are no longer in need of purification.
As to those in Purgatory, while the Mass, being the application of and the re-presenting of the sacrifice of the cross in an unbloody manner, is the most effecatious means of applying grace to a soul in purgatory, it is not the only way we can merit graces for them (See the sermon portion from Fr. Roberts in order to clarify merit).
As to the Sacraments, they cannot be bought or sold, masses are not to be sold; however it is customary to give a stipend for the priest’s time, candles, wine and hosts which have to be replenished, etc. In the middle ages it was a custom to give a priest what would have consisted of two meals (or the cost of two meals) for his offering the mass for your intentions. While a priest can very well offer a mass, and not take a stipend for it, once he has accepted a stipend or accepts to offer the Mass, he has a moral obligation to offer that Mass. In most places the legislation of the Church is within a reasonable time, ie thirty days. There are other provisions, such as perpetual Masses, where the Mass may be offered once a year on the anniversary of the death. If a parish or priest cannot accomodate the Masses in a reasonable time, there are many missionary priests in poor countries who can offer the Mass and are in great need of stipends just to live. I myself prefer to send mass intentions (and stipends) to these brave men who put life and comfort aside in order to carry the message of Christ to the ends of the earth.
There is no telling from the story you read on the internet who told this person about a “two year waiting list” or how they broached the subject of “paying” for masses. It is sometimes hard to determine who in such events is misinformed.