I'm no expert but seems like a fair offer. I don't like verts, but they always get more money. I'd stick to no more than $15k because of the ABS issue (you can talk that up all day as an unknown). Looks like all the need to do mods are already done, so nice. Go for it. All they can say is no. Make sure you get a copy of the tune (I'm assuming it isn't stock). Sometimes being close to home is worth a little extra.
You can also look at the "sold" auctions on ebay to see other real world values.
2008 Bullitt|Roush M90 w/2.57 pulley & CAI; 90mm MAF; Steeda-UCA, LCAs, Ultralites, links, mounts; MM CC plates; Bilsteins; GT500 FCAs; Brembos; Roush shifter; GT500KR axle back; etc
1969 Coupe Restomod-never complete!
2008 Power Wheels Bullitt Clone
Mustangs from the past: 66 coupe, 69 Coupe, 69 Grande, 2001 Bullitt, 2011 V6