[GQ][ON] Help determining pricing for used GBBR

Hey there! I'm reaching out cause I wanted your guys' opinions on how to properly price out a GBBR. I have a used WE Apache A2, in great condition despite some scuffs from it being gamed 5-6 times. Plus 4 additional magazines in good condition, and a drum-magazine that needs it's O-Rings replaced. I'm looking to sell it soon, but figured it would be best to get advice on how to estimate it's value. Any help would be so greatly appreciated. Thank you!