Try this for a quick serial number check --> www.biggerhammer.net/ar15/ar15serial.html
Indication is that this is pre-ban.
To be safe, always call the manuafacturer if possible.
From your description, it is a blue label rifle, which means no bayo lug, sear-blocked lower. The mags are probably worth $80 - $100 a piece by themselves. I frequently see blue label rifles around $1400 - 1700, though usually not with so many Colt mags. Green label rifles I've seen for $1600 - $2000.
I have one of these, and they are fun and accurate, especially with zippier rounds. It is also a plus if your indoor range does not allow rifle calibers because ranges will usually let you shoot pistol caliber rifles.
Hope this helps.