Is $9,000 to remediate mold in attic a fair price?

I went into my attic to investigate a small leak near the chimney collar above my garage and found visible mold on the roof sheathing. While I was up there, I also noticed that the bathroom exhaust duct had become disconnected, dumping moist air directly into the attic (that is fixed now). I had a roofer look, and he said the root cause seems to be poor attic ventilation. The soffits are blocked with insulation, and there’s only a 20-foot ridge vent. I plan to address this by unblocking soffits, adding baffle vents, and possibly extending the ridge vent. I'm stuck on how to proceed with mold remediation and roof replacement. I got a $9k quote from a mold company, but all they did was stick their head in the attic and assume the mold was everywhere. They proposed spraying it and doing a HEPA vacuum. I also got a quote for $15k to replace the sheathing and the entire roof system (1500 sq ft), but a roofing friend told me the shingles still have 5–10 years of life, so it may be premature to replace the whole roof. I've also considered treating the mold myself with a mold cleaner and fixing the ventilation issues. I'm questioning if replacing the roof would be overkill if the mold is localized, if anyone has had success with DIY mold treatment in attics, if it's worth replacing the insulation if it’s been exposed to mold, and if there are any red flags in the advice I’ve gotten so far.