I just looked around using Google and seen that Colt R6530 Sporter Lightweight carbine sells at a range of from low $1K up to $1,500 on the high side, mostly excellent to new (new in box) condition.
Your carbine is an early R6530 model, I used to have the same as yours except mine had the "CS" marked A1 short length fixed stock.
Early in their production Colt used the slab side A1 type lowers with large hole pivot pins and the short A1 length fixed stock, later models they used A2 type lowers with fence around the mag release button, small pivot pins, large FCG pins, and longer A2 fixed stock, that model was made from 1990 to '94.
The R6530 carbine was replaced by the Match Target series MT6530 model without the A2 flash suppressor around 1994 which was the start of the assault weapons ban era.
BTW, I had been at that Martin B. Retting gun store in the Culver City, CA (L.A. area) in the '90s when I was still living there that time, it is a large gun shop with plenty of expensive guns and have a pretty good selection.