No, that is not normal, it's an unusually high kill rate in my experience. When I've been in parties that hit those levels, there have usually been one or two kills per campaign that require resurrection (though more close saves with resurgences and whatnot).
It may be due to bad player tactics, weak characters, or the GM runs things tougher than the average GM - either "higher CR" or just "better", some GMs (like myself) manage to squeeze a lot more kill per hit die out of opponents. Sometimes a GM runs a harder game, which is fine.
But of course the thing about high level D&D is that you have multiple levels of defense against death, so as long as it's not impacting the fun, there's nothing really wrong with it. You get to play croquet with the angels on a regular basis, heck, that could be part of the plotline (Order of the Stick, anyone?)
If you do want to do something about it, and don't want to embrace character optimization, I would review the results of combats with the rest of the group and see if the deaths were preventable - do party fighters repeatedly charge recklessly into combat, ruining the ability of mages to area effect; do you get spread out all over the battlefield where the cleric can't effectively help you when you're in trouble; do characters not participate well (the tank fighter who hides in the back, the cleric who's too busy fighting to heal)?
Tactics In Depth
I had to coach one player group that was getting demoralized about how tough combats were going in one D&D campaign. In general they didn't have any coordination - they'd open a door and see bad guys. One guy would run in (before the mages could cast damage or battlefield control spells), others would back off, people didn't have mobility or line of sight. They'd decide to run, except most of the group would retreat, but one guy would want just one more round of full attacking, and then be cut off, and then half of the rest of the party would keep fleeing but the other half would come back and help them, and get cut off themselves... I taught them to do simple things like NOT go in the door, but back off and form an inverted triangle around the door and let them come to the party (for dumb melee opponents of course) so that they are the ones getting surrounded and losing actions and being separated. One PC that was taking on a leadership role took it upon themselves to "call the shots" in combat so that a retreat or attack was performed by the whole group. There's a lot of D&D-specific ticky combat tactics stuff, but I always see the greatest difference being made by system-independent "having your crap together" kinds of basic techniques. Have patience, don't get split up, coordinate maneuver to take the fewest attacks but deliver the most, concentrate fire.
I remember in one five year long 2e campaign I ran, the team leader went so far as to run IA drills and basic response plans. When they would come into contact, there were set formations they would move into automatically. The shouted command "Blue" told PCs to close their eyes to avoid the mage's Color Spray. The only PC death in that campaign came from PC on PC action.
It does not.
Insanity is a 7th level spell. Prismatic Spray is a 7th level spell. Neither are dispelled by Dispel Magic nor Stone To Flesh (although you could use Dispel Magic to attempt to counter Prismatic Spray as it is cast, as normal). They are too powerful for Break Enchantment to break, because they're not 5th level or lower. From Break Enchantment:
If the spell is one that cannot be dispelled by dispel magic, break enchantment works only if that spell is 5th level or lower.
As you've noticed, Insanity actually lists what can cure it. From the Pathfinder SRD:
Greater restoration, heal, limited wish, miracle, or wish can restore the creature.
Best Answer
Single use item
A scroll (6125 gp) or an item with one charge (5675 gp) is probably the cheapest solution to cast Raise Dead.
Also, you can use these items with Use Magic Device. Chances are lower than for a lower-level-than-necessary cleric, but you can retry (with 24h break on natural 1) for sure. (I'd say that - although not very clearly - retries for casting spells from scrolls are possible too). Raise Dead is not a combat spell anyway (casting time 1 minute), so the impact of several retries is not essential.
Ring of Spell Storing
More expensive option, requiring some balancing role-playing, is to give your NPC (or a temple the PCs can visit) a Ring of Spell Storing (50k gp) with Raise Dead. (Imagine a more powerful cleric recharging the ring every time she visits the temple, but not too often). The advantage of the ring - anyone can have it and use it, even if your local temple is run by a Lvl 1 Paladin (here you need the balancing act - 50k gp, powerful item is unusual in the hands of a 1st level character).
Planar Ally (long shot)
Lesser Planar Ally is a 4th level Cleric spell with 100 XP cost. A scroll is 1200 gp, a wand is 920 gp per charge. A summoned planar ally requires a payment of 100gp per HD for quick tasks, half if the task is not hazardous.
And a Hollyphant (Book of Exalted Deeds, p. 176) and a Movanic (Fiend Folio, p. 57) are 6HD, good outsiders (Hollyphant - NG, Movanic - any good) that happen to have Raise Dead as a spell-like ability. You could allow the NPC to be able to call them with Lesser Planar Ally and pay either 300gp (I don't think it's hazardous) or bargain another service for the outsider. With a scroll, the total cost is 1500 gp.
You could assume your (or the NPCs) deity will send one of these outsiders if you request help to bring someone back from the dead.