Look at it this way: PCs are rich and powerful. They don't have to pay anymore. Retail healing is for peasants.
How about this (kinda plot-hooky):
Good temples that aren't dealing with the PCs ask for money so they can pay back the community. The fee is based on how much you can afford and how much you need the service. (No Quests to make that girl go to prom with you!) They take that money and spread it around town. Nice and progressive. This might mean that the PCs get some freebies from the temple at low-levels, or when things are dire. It also means that spell costs will scale with level.
Neutral temples are in it for themselves, so they take the money and help themselves out. It's a service, supply and demand, the whole thing.
Now we come to Evil temples. You'd think that Evil temples would be the worst of the lot. But no, they are the nicest guys around (for the most part). When they operate in the "Good" lands of humans, halflings, etc. they are all smiles and kisses. They spread around as much magic as they can, all of it for free.
Why? Because it gets them in with the population. The peasants see no difference between the Good temple and the Evil one. There isn't really any difference in how they go about things. Except every now and then, when they are delivering their sermons, they slip in some bad advice that they know people will take in the wrong way. It's all meant to make people go Evil over time. First it's things like, "Why not cheat on your wife? You're only human after all; to repress your urges is wrong." Then they ramp it up to the real Evil stuff.
They also do a lot of things that the Good temple wouldn't think about. Stuff like the Quest spell to make the girl fall in love with you. (That would be one sick spell. And if the guy complains - I didn't want a slave! - you just make sure that if he spills the beans everyone in town is going to know what he did. And that you cast a Good spell that was corrupted by his evil intentions. Sucker.)
So give this "new" religion a few years of moving slowly, evil guys on the frontiers all worked up to increase the pressure on the Good lands (so they'll be more tempted to take Evil actions because of need), and soon you'll have your own little empire.
Go Vecna!