Personally, I've only played one game in the past 20 years where coming back from the dead was a possibility.
The current group I'm with decided they didn't want to be able to come back from the dead, they'd just make new characters. So I haven't had a chance to try the rules that I was planning on using. But this is what I was thinking:
There's dead, and then there's Dead. If a person has their brain destroyed or their spinal column severed (like what happens from a broken neck, or by a weapon), there's no coming back. There's also no coming back if the person was killed using a soul sucking weapon. If a person dies because of age, there's no coming back. There's certain spells that can be employed to prevent a person from coming back. The only way to deal with that is to find the person that's cast the spell and either have them remove it or kill them and cause the enchantment to fail
A person can stay dead for a number of [your time preference] equal to their level. Once that time has expired, it's all over. I personally think [days] is good.
When a person comes back, they're at a penalty for all their actions equal to the amount of time they stayed dead. They penalty is reduced by one for every day of recovery, until the penalty is completely eliminated. Nothing can speed this up, and if the character is doing "strenuous" activities it delays the recovery by another day.
For example, in my game I'd use [days] as the time delay. Say a character that's 10th level was killed. The brain and spine are still intact, so there's a total of 10 days they've got to have the character brought back. For whatever reason the character is brought back on the final day possible (day 10).
When the character is brought back, they're at a -10 for all activities. They can putter about doing very light stuff and that's about it. The next day, they're at a -9. And so forth until the penalty is eliminated. If they're off doing combat or whatever else the GM deems is "strenuous", then they don't get that day as a Recovery day.
I don't see a need to try and mechanically limit the amount of times someone can be brought back, other than the ways I've outlined above. It means that someone can die, and someone can be made permanently dead if there's a reason to do so. The world effectively has coming back from the dead be an option for everyone, but it doesn't mean that people can't be assassinated permanently.
Deliberately making someone unable to come back from the dead is going to be a Big Deal and you'd better have a good reason for doing it if you're caught. Being able to get someone brought back from the dead is really just a matter of money. Money up front of course. In gods we trust, all others pay full cash.
As I see it, the nobility don't have a problem being able to pay the fee. For them death is mostly a matter of an inconvenience. A potentially serious one, but still nothing too bad. If someone made them dead, it was either part of a duel or it's a message. Duels are for honor, and a message means they'd better seriously reconsider whatever it is that they're doing.
For the middle class it's a more serious business. Chances are they're not doing anything to really piss someone off enough to have them killed. So it's probably an accident of some sort or another. Cost-wise, it's going to hurt but it's doable.
Poor people... *shrug*... they get screwed over as normal.
Important note: Coming back from the dead isn't a clerical thing. Yes, that's right. Clerics don't have anything to do with bringing people back from the dead.
Why?
Because the gods aren't exactly keen on it. They collect souls for their own reasons. The last thing they really want is some hairless monkey coming up to them and whining "We really like Bob. Could you please give him back to us?" Screw that. They lose a soul, it could be gone permanently. The person might take to worshiping another god, some soul sucking thing might get hold of the person brought back, or whatever. Gods don't like the fact that an end run can be made around death. Even in a limited fashion. Once they get hold of a soul, they're not planning on letting go of it.