Here in Michigan at the Dealer it will run you about 6,000

If it matters, I have a 2004 4Runner and have been on the search for the claimed head gasket issue. At about 185k miles my engine had rough start-up crank, vsc & trac lights came on, and decided to change all the spark plugs. No I hadn't followed proper maintenance & yes they were charcoal black. The problem seemed better but I noticed that the engine would run hot when in idle, like in parking lot. So I added radiator fluid. As it got extremely hot and humid in the summer, above 90F, the rough start-up was again prominent. Computer said cylinder6 misfire. So I let a mechanic see it. He said that oil was leaking into cylinder 6. May need head gasket but try oil additive. I do not remember which one. I took it to Toyota & they wanted my car for trade-in or I would need a new engine. I laughed. I did the oil additive and then changed the oil. Problem was gone. Then it came back. So I changed ignition coil pack number6. Done so I thought, but the weather was cooling down outside. Started making sure to get the correct oil no more quickie-lubes & no walmart. Problem seemed fixed & drove the vehicle to Missouri from Georgia the car was running great. Then in the winter the engine temp shot to hot, the radiator reservoir was a dry desert. I could go about 6 months before needing to add radiator fluid. The spark plugs and initial things happened in 2013 I had no start-up issues until 2016.this time when the rough start-up happened my engine would get hot. Toyota said ignition coil #4 replacement. Ok did that & the problem came back a week later. The 2nd time they said its head gasket wanted almost $6000. They told me radiator fluid was dripping into the cylinders causing misfire or some jargon. I stopped listening at $6k.
Ok so I'm not a mechanic but I'm not stupid either and if the radiator is getting low meaning no fluid how is there available fluid to cause a misfire? Wouldn't the misfire occur when there is a full radiator? By the way my 4Runner had 230,000miles by now. The mechanic I took it to, one of the best I've met, said radiator is busted. It was too hard to notice, at the top he showed me. Radiator replaced august2016. Drove to GA then FL and back to GA when engine started shaking when pressing gas, 8miles away from destination. Called that mechanic in Mo he said its coil pack. So coil pack #6 bad again, it was 3yrs old. Got back to MO and have replaced ignition coil pack #2. The startup problem is gone but the lights are there even after I disconnected the battery, so I think I have to replace the 1, 3, & 5 coil packs soon. After all the forums, I still have a hard time believing the head gasket is bad bc 1. My oil is NEVER milky, & I change it every 5,000-6,000 miles I check it at 4,000 to see if it's dirty., 2. There is no smoke out the exhaust and I might blame that on the catalytic converter since I have experienced the rotten egg smell., 3. I can get a speeding ticket & my engine never looses power when I use a lead foot. I never changed the transmission fluid until 2016 bc the Toyota guy convinced me of it. I see the recommendations as guides or a checklist. I have heard the trickling noise and clicking noise when the a/c is running. Just last week while in a drive through my engine got hot but I turned the heat on and the temp dropped. My guess is a fan or motor or electrical, bc the radiator was full when I got home. I hope this helps someone or someone can help me. I have heard that sensors can cause false codes seeming like issues. Ultimately I think I had two different things going on, electrical & radiator. A guy I know who has a Subaru had his head gasket replaced & he had problems driving down the road due to power loss and said it was obvious & it got bad quick.
I love my 2004 4Runner and hate the 2016 model, there's no cassette player...lol.

I certainly don't want to sound discouraging, but it's likely at least one problem is a blown head gasket. I have an '04 SR5 that started shuddering when cold and when traveling at about 1500 rpm under a mild load. The VSC light and check engine light appeared. I checked it and found my #6 cylinder was mis firing. Changed the #3 and 6 coil wires but this didn't fix it. Brought it in for a leak down test, confirming it was a failed head gasket. Should be around a $2K fix so $6K is outrageous. One the plane the heads and replace the gaskets, it's likely you'll get another 200K miles out of it. I believe these years had a faulty head gasket by Toyota that was later rectified. Don't give up!


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Old update: I replaced the last couple of coil packs the vibration is gone.
If you replace one you need to replace the rest soon after. You replace all the spark plugs at one time, but you don't replace all the coil packs, why?
The engine did get warm once in the dead of summer, like 100degrees outside. I burped the new radiator and good to go. I think it's a computer issue. The old coil pack fails and triggers it. VSC comes on bc of vibration. Glad that works. Check engine comes on bc of misfire. The other old coil packs don't perform as efficient which computer tracks & flags the issue.
From all the head gasket stories and experienced mechanics tell me that if it's a head gasket issue you'll know it bc it will get bad quick.
It seems more likely a cheaper cost component faulting; radiators crack possibly due to being dirty, so dont drive in the mud lol. Anyhow mine has 260,000miles, 14yrs old, and the problem (not dead on road problem) started 5yrs ago - gone now. It is likely the head gasket repairs for others were warranted, different situations maybe.
I'm sure someone will have a negative comment but I'm not the one messing with the head gasket.

We just went through this with my daughters 4Runner at about 178000 miles. We did OEM spark plugs, wires, and cylinder 6 coil pack. It still was throwing the code and vibrating terribly so we took to a good mechanic. He found the injector clogged for cyl 6. For Toyota to warranty the replacement injector, he also had to change the fuel filter. And he said the filter was dirty! So, change your fuel filters every 80k miles because that was probably the culprit. He also said if you run it long like that, it can cause engine damage.