But I've heard horror stories of 250-300k..and planes being held hostage for the money, even though the original quote was "below 100k"
You do realize that "your baby" is taken apart completely a the 12 years and that when something like corrosion etc is found in places normally not inspected out side the 12 y inspection, the price MUST go up. No mx shop worth a dime will give you a FIXED quote on this kind of job without provisions made for findings.
300k/12y = 25.000USD /yr. If you cant afford that....