Condition? Scope? Flash hider? Flip up muzzle protector? Matching? Condition (yes, twice, since this seems to be so important to pricing a 99)? Rear monopod?
Gun price varies drastically with condition. My guess on extras - $2k each per conversion (including barrel). $1500 for extra mag. Maybe $500 for conversion mags. Added together ~$6k for extras. I may be low on these since I've not seen any in a while, so between $6-$8k for extras to the right buyer. Hard to tell current temperature / interest for Japanese NFA.
Not familiar with ballistic shield?
Gun maybe between $12 and $20k+ depending on condition? Others may have different opinions. Good luck!