I know this was an old thread but Congrats anyway!
Nice new old stock, what a great find.
My first Colt R6600 AR-15A2 HBAR Sporter rifle I used to have got it new in 1986 for if I remember correctly in the $500 price range that time.
My HBAR was my 4th Colt AR, my first was my SP1 in 1971, second is a Sporter II model 6401 AR-15A2 rifle in 1984, and my third was a Sporter II A2 carbine in 1985.
I mainly used my HBAR rifle for DCM rifle competition (CMP now) and I had it steadily modified from lower pull weight & smoother trigger, NM match narrower and smaller aperture sights, free floating tube with modified A2 handguards, then in the early 1990s I worn out the barrel and changed it to a Douglas SS match barrel.
I sold mine in 2001 because I was not competing anymore since I had my first son in 1996, and because there was a ban that time I got a great price for my pre ban rifle.