I have Chiari. I'm honestly not the best source for what is considered a "major" symptom of Chiari. It is a degenerative disease, and I think part of it is that some people don't get diagnosed until they've had it for years or even decades & eventually I many people who develop symptoms do end up with pain either in the back of their head or their neck. For me, the first symptoms weren't headaches. I had a history of the so-called "silent migraines" & was seeing a neurologist for that, but we're not sure whether that was related to the Chiari.
First symptom was vertigo. Vertigo, especially when it is not based in the ear, often causes a feeling of fullness or pressure in the back of the head & pain around the eyes b/c of overcompensation of the visual sense for the failure of other senses to coordinate balance. Eventually (a few years later), I did start getting headaches, primarily with lifting -- also with coughing & sneezing. Some of them actually were migraines, & could be treated with imitrex or such, but most were the "chiari" headaches. The chiari headaches really were more like a throbbing pressure at the base of my skull. While bothersome, they were not especially painful. Symptoms progressed over time & I started to develop slurred speech (over another year or so). The vertigo got worse & worse. I started having problems with seeing black spots and also developed some minor issues with turning door knobs and the like.
I had surgery a while back to remedy the situation, but not all the symptoms are reversible. The main thing I would look to consider chiari as a diagnosis is whether symptoms were preceded by either whiplash or a fall, or in certain cases riding roller coasters a lot. Chairi is far more common in females than males & usually first shows up between 20's to mid-30's. Only 10-20% of people with the malformation develop symptoms. If you mostly fit those criteria & have noticed a progression, even if it's very slow, maybe it would be worthwhile to save up to get an MRI. Otherwise, I'd say it's probably not worth the money since you don't have insurance. Sorry I don't have any ideas for you. Wish I could be more help. :)