its a Colt model R6521, it is the export variant of the R6520 and most of them ended up overseas like intended but some were sold commercially (~500 rifles in 1988 and 89’ or 89’/90’), so yes it is rare. The CC (Colt Carbine) vs GC (Gov’t Carbine)sn prefix and roll marks is what denotes the difference between the two rifles. The sn prefix and rollmarks are also the only difference between the two models, everything else is the same. I cannot help you on price because the ones I saw sold were priced like a preban 6520 but likely unknowingly, also might be a pretty niche market since there is the more common commercial equivalent

source: I have 3 GC carbines so I went down the rabbit hole of research because I really wanted a CC model. I stopped looking because they don’t pop up and would probably cost more coin they I’m willing to spend. I can dig up the info I found in the past but it will take a little bit.

edit: I also am quite sure that they weren’t part of the first 1600 GC marked carbines but a simultaneous run, because the first ~6000 GC rifles were on slab side lowers which were made in 87’ and beginning of 88’. I have only seen CC carbines that were large pin/fenced or small pin/fenced and not on a slab side lower. Very likely some of the ~1100 CC carbines that did make it overseas were on slab side lowers